diff --git a/lib/mailerlite/automations/automations.rb b/lib/mailerlite/automations/automations.rb
index 1889e69..00baa3e 100644
--- a/lib/mailerlite/automations/automations.rb
+++ b/lib/mailerlite/automations/automations.rb
@@ -25,7 +25,7 @@ def get(limit: nil, page: nil, filter: {})
       params['filter[group]'] = filter[:group] if filter.key?(:group)
       params['limit'] = limit if limit
       params['page'] = page if page
-      uri = URI("#{API_URL}/automations")
+      uri = URI("#{MAILERLITE_API_URL}/automations")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -35,7 +35,7 @@ def get(limit: nil, page: nil, filter: {})
     # @param automation_id [String] the ID of the Automation to fetch
     # @return [HTTP::Response] the response from the API
     def fetch(automation_id)
-      client.http.get("#{API_URL}/automations/#{automation_id}")
+      client.http.get("#{MAILERLITE_API_URL}/automations/#{automation_id}")
     end
 
     # get_subscriber_activity the subscriber activity for specified Automation
@@ -54,7 +54,7 @@ def get_subscriber_activity(automation_id:, filter: {}, page: nil, limit: nil)
       params['filter[keyword]'] = filter[:keyword] if filter.key?(:keyword)
       params['page'] = page if page
       params['limit'] = limit if limit
-      uri = URI("#{API_URL}/automations/#{automation_id}/activity")
+      uri = URI("#{MAILERLITE_API_URL}/automations/#{automation_id}/activity")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
diff --git a/lib/mailerlite/batch/batch.rb b/lib/mailerlite/batch/batch.rb
index a5db28e..2c95cbc 100644
--- a/lib/mailerlite/batch/batch.rb
+++ b/lib/mailerlite/batch/batch.rb
@@ -18,7 +18,7 @@ def initialize(client: MailerLite::Client.new)
     # @return [HTTP::Response] the response from the API
     def request(requests:)
       params = { requests: requests }
-      client.http.post("#{API_URL}/batch", body: params.to_json)
+      client.http.post("#{MAILERLITE_API_URL}/batch", body: params.to_json)
     end
   end
 end
diff --git a/lib/mailerlite/campaigns/campaigns.rb b/lib/mailerlite/campaigns/campaigns.rb
index f7143db..e08ee11 100644
--- a/lib/mailerlite/campaigns/campaigns.rb
+++ b/lib/mailerlite/campaigns/campaigns.rb
@@ -24,7 +24,7 @@ def get(filter:, limit: nil, page: nil)
       params['filter[type]'] = filter[:type] if filter.key?(:type)
       params['limit'] = limit if limit
       params['page'] = page if page
-      uri = URI("#{API_URL}/campaigns")
+      uri = URI("#{MAILERLITE_API_URL}/campaigns")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -78,7 +78,7 @@ def create(name:, type:, emails:, language_id: nil, groups: nil, segments: nil,
         }
       end
 
-      client.http.post("#{API_URL}/campaigns", body: params.compact.to_json)
+      client.http.post("#{MAILERLITE_API_URL}/campaigns", body: params.compact.to_json)
     end
 
     # Update a new campaign with the specified details.
@@ -132,7 +132,7 @@ def update(campaign_id:, name:, type:, emails:, language_id: nil, groups: nil, s
 
       end
 
-      client.http.put("#{API_URL}/campaigns/#{campaign_id}", body: params.compact.to_json)
+      client.http.put("#{MAILERLITE_API_URL}/campaigns/#{campaign_id}", body: params.compact.to_json)
     end
 
     # Schedules the specified campaign.
@@ -160,7 +160,7 @@ def schedule(campaign_id:, delivery:, schedule: nil, resend: nil)
       params['resend']['minutes'] = resend[:minutes] if resend&.key?(:minutes)
       params['resend']['timezone_id'] = resend[:timezone_id] if resend&.key?(:timezone_id)
 
-      client.http.post("#{API_URL}/campaigns/#{campaign_id}/schedule", body: params.compact.to_json)
+      client.http.post("#{MAILERLITE_API_URL}/campaigns/#{campaign_id}/schedule", body: params.compact.to_json)
     end
 
     # Returns the details of the specified Campaigns
@@ -168,7 +168,7 @@ def schedule(campaign_id:, delivery:, schedule: nil, resend: nil)
     # @param campaign_id [String] the ID of the campaign to fetch
     # @return [HTTP::Response] the response from the API
     def fetch(campaign_id)
-      client.http.get("#{API_URL}/campaigns/#{campaign_id}")
+      client.http.get("#{MAILERLITE_API_URL}/campaigns/#{campaign_id}")
     end
 
     # Cancels the specified campaign.
@@ -176,7 +176,7 @@ def fetch(campaign_id)
     # @param campaign_id [String] the ID of the campaign to delete
     # @return [HTTP::Response] the response from the API
     def cancel(campaign_id)
-      client.http.post("#{API_URL}/campaigns/#{campaign_id}/cancel")
+      client.http.post("#{MAILERLITE_API_URL}/campaigns/#{campaign_id}/cancel")
     end
 
     # Deletes the specified campaign.
@@ -184,7 +184,7 @@ def cancel(campaign_id)
     # @param campaign_id [String] the ID of the campaign to delete
     # @return [HTTP::Response] the response from the API
     def delete(campaign_id)
-      client.http.delete("#{API_URL}/campaigns/#{campaign_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/campaigns/#{campaign_id}")
     end
 
     # activity the subscriber activity for specified campaign
@@ -203,14 +203,14 @@ def activity(campaign_id:, filter: nil, page: nil, limit: nil, sort: nil)
       params['page'] = page if page
       params['limit'] = limit if limit
       params['sort'] = sort if sort
-      client.http.post("#{API_URL}/campaigns/#{campaign_id}/reports/subscriber-activity", body: params.compact.to_json)
+      client.http.post("#{MAILERLITE_API_URL}/campaigns/#{campaign_id}/reports/subscriber-activity", body: params.compact.to_json)
     end
 
     # Get a list of all campaign languages available
     #
     # @return [HTTP::Response] the response from the API
     def languages
-      client.http.get("#{API_URL}/campaigns/languages")
+      client.http.get("#{MAILERLITE_API_URL}/campaigns/languages")
     end
   end
 end
diff --git a/lib/mailerlite/client.rb b/lib/mailerlite/client.rb
index 09651d2..09ab26d 100644
--- a/lib/mailerlite/client.rb
+++ b/lib/mailerlite/client.rb
@@ -3,7 +3,7 @@
 require 'http'
 require 'dotenv/load'
 
-API_URL = 'https://connect.mailerlite.com/api'
+MAILERLITE_API_URL = 'https://connect.mailerlite.com/api'
 
 Dotenv.require_keys('MAILERLITE_API_TOKEN')
 
diff --git a/lib/mailerlite/fields/fields.rb b/lib/mailerlite/fields/fields.rb
index 50e4e23..23babe0 100644
--- a/lib/mailerlite/fields/fields.rb
+++ b/lib/mailerlite/fields/fields.rb
@@ -25,7 +25,7 @@ def get(limit: nil, page: nil, filter: {}, sort: nil)
       params['sort'] = sort if sort
       params['limit'] = limit if limit
       params['page'] = page if page
-      uri = URI("#{API_URL}/fields")
+      uri = URI("#{MAILERLITE_API_URL}/fields")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -37,7 +37,7 @@ def get(limit: nil, page: nil, filter: {}, sort: nil)
     # @return [HTTP::Response] the response from the API
     def create(type:, name:)
       params = { 'name' => name, 'type' => type }
-      client.http.post("#{API_URL}/fields", json: params.compact)
+      client.http.post("#{MAILERLITE_API_URL}/fields", json: params.compact)
     end
 
     # Update the specified Field
@@ -47,7 +47,7 @@ def create(type:, name:)
     # @return [HTTP::Response] the response from the API
     def update(field_id:, name:)
       params = { 'name' => name }
-      client.http.put("#{API_URL}/fields/#{field_id}", json: params.compact)
+      client.http.put("#{MAILERLITE_API_URL}/fields/#{field_id}", json: params.compact)
     end
 
     # Deletes the specified Field.
@@ -55,7 +55,7 @@ def update(field_id:, name:)
     # @param field_id [String] the ID of the Field to delete
     # @return [HTTP::Response] the response from the API
     def delete(field_id)
-      client.http.delete("#{API_URL}/fields/#{field_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/fields/#{field_id}")
     end
   end
 end
diff --git a/lib/mailerlite/forms/forms.rb b/lib/mailerlite/forms/forms.rb
index 52300fd..69f008e 100644
--- a/lib/mailerlite/forms/forms.rb
+++ b/lib/mailerlite/forms/forms.rb
@@ -24,7 +24,7 @@ def list(type:, filter: {}, limit: nil, sort: nil, page: nil)
       params['limit'] = limit if limit
       params['sort'] = sort if sort
       params['page'] = page if page
-      uri = URI("#{API_URL}/forms/#{type}")
+      uri = URI("#{MAILERLITE_API_URL}/forms/#{type}")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -34,7 +34,7 @@ def list(type:, filter: {}, limit: nil, sort: nil, page: nil)
     # @param form_id [String] the ID of the forms to fetch
     # @return [HTTP::Response] the response from the API
     def fetch(form_id)
-      client.http.get("#{API_URL}/forms/#{form_id}")
+      client.http.get("#{MAILERLITE_API_URL}/forms/#{form_id}")
     end
 
     # Returns the subscribers who signed up to a specific form
@@ -42,7 +42,7 @@ def fetch(form_id)
     # @param form_id [String] the ID of the forms to fetch
     # @return [HTTP::Response] the response from the API
     def fetch_subscribers(form_id)
-      client.http.get("#{API_URL}/forms/#{form_id}/subscribers")
+      client.http.get("#{MAILERLITE_API_URL}/forms/#{form_id}/subscribers")
     end
 
     # Update the specified Forms
@@ -52,14 +52,14 @@ def fetch_subscribers(form_id)
     # @return [HTTP::Response] the response from the API
     def update(form_id:, name:)
       params = { 'name' => name }
-      client.http.put("#{API_URL}/forms/#{form_id}", json: params.compact)
+      client.http.put("#{MAILERLITE_API_URL}/forms/#{form_id}", json: params.compact)
     end
 
     # Returns the total number of Forms in the MailerLite account.
     #
     # @return [HTTP::Response] the response from the API
     def fetch_count
-      client.http.get("#{API_URL}/forms/?limit=0")
+      client.http.get("#{MAILERLITE_API_URL}/forms/?limit=0")
     end
 
     # Deletes the specified forms.
@@ -67,7 +67,7 @@ def fetch_count
     # @param form_id [String] the ID of the forms to delete
     # @return [HTTP::Response] the response from the API
     def delete(form_id)
-      client.http.delete("#{API_URL}/forms/#{form_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/forms/#{form_id}")
     end
   end
 end
diff --git a/lib/mailerlite/groups/groups.rb b/lib/mailerlite/groups/groups.rb
index 8db2b2e..bc86d07 100644
--- a/lib/mailerlite/groups/groups.rb
+++ b/lib/mailerlite/groups/groups.rb
@@ -24,7 +24,7 @@ def get(filter: {}, limit: nil, sort: nil, page: nil)
       params['limit'] = limit if limit
       params['sort'] = sort if sort
       params['page'] = page if page
-      uri = URI("#{API_URL}/groups")
+      uri = URI("#{MAILERLITE_API_URL}/groups")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -35,7 +35,7 @@ def get(filter: {}, limit: nil, sort: nil, page: nil)
     # @return [HTTP::Response] the response from the API
     def create(name:)
       params = { 'name' => name }
-      client.http.post("#{API_URL}/groups", json: params.compact)
+      client.http.post("#{MAILERLITE_API_URL}/groups", json: params.compact)
     end
 
     # Update the specified Group
@@ -45,7 +45,7 @@ def create(name:)
     # @return [HTTP::Response] the response from the API
     def update(group_id:, name:)
       params = { 'name' => name }
-      client.http.put("#{API_URL}/groups/#{group_id}", json: params.compact)
+      client.http.put("#{MAILERLITE_API_URL}/groups/#{group_id}", json: params.compact)
     end
 
     # Get Subscribers assigned to the specified group.
@@ -60,7 +60,7 @@ def get_subscribers(group_id:, filter: {}, limit: nil, page: nil, sort: nil)
       params['limit'] = limit if limit
       params['sort'] = sort if sort
       params['page'] = page if page
-      client.http.get("#{API_URL}/groups/#{group_id}/subscribers", json: params.compact)
+      client.http.get("#{MAILERLITE_API_URL}/groups/#{group_id}/subscribers", json: params.compact)
     end
 
     # Assign Subscriber to the specified group.
@@ -68,7 +68,7 @@ def get_subscribers(group_id:, filter: {}, limit: nil, page: nil, sort: nil)
     # @param subscriber [Integer] The id of existing subscriber belonging to the account
     # @return [HTTP::Response] the response from the API
     def assign_subscriber(group_id:, subscriber:)
-      client.http.post("#{API_URL}/subscribers/#{subscriber}/groups/#{group_id}")
+      client.http.post("#{MAILERLITE_API_URL}/subscribers/#{subscriber}/groups/#{group_id}")
     end
 
     # Unassign Subscriber to the specified group.
@@ -76,7 +76,7 @@ def assign_subscriber(group_id:, subscriber:)
     # @param subscriber [Integer] The id of existing subscriber belonging to the account
     # @return [HTTP::Response] the response from the API
     def unassign_subscriber(group_id:, subscriber:)
-      client.http.delete("#{API_URL}/subscribers/#{subscriber}/groups/#{group_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/subscribers/#{subscriber}/groups/#{group_id}")
     end
 
     # Deletes the specified Groups.
@@ -84,7 +84,7 @@ def unassign_subscriber(group_id:, subscriber:)
     # @param group_id [String] the ID of the Groups to delete
     # @return [HTTP::Response] the response from the API
     def delete(group_id)
-      client.http.delete("#{API_URL}/groups/#{group_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/groups/#{group_id}")
     end
   end
 end
diff --git a/lib/mailerlite/segments/segments.rb b/lib/mailerlite/segments/segments.rb
index 9e23b29..052c427 100644
--- a/lib/mailerlite/segments/segments.rb
+++ b/lib/mailerlite/segments/segments.rb
@@ -22,7 +22,7 @@ def list(limit: nil, page: nil)
       params['limit'] = limit if limit
       params['page'] = page if page
 
-      client.http.get("#{API_URL}/segments", json: params.compact)
+      client.http.get("#{MAILERLITE_API_URL}/segments", json: params.compact)
     end
 
     # Update the specified Segment
@@ -32,7 +32,7 @@ def list(limit: nil, page: nil)
     # @return [HTTP::Response] the response from the API
     def update(segment_id:, name:)
       params = { 'name' => name }
-      client.http.put("#{API_URL}/segments/#{segment_id}", json: params.compact)
+      client.http.put("#{MAILERLITE_API_URL}/segments/#{segment_id}", json: params.compact)
     end
 
     # Get Subscribers assigned to the specified Segment.
@@ -46,7 +46,7 @@ def get_subscribers(segment_id:, filter: {}, limit: nil, after: nil)
       params['filter[status]'] = filter[:status] if filter.key?(:status)
       params['limit'] = limit if limit
       params['after'] = after if after
-      uri = URI("#{API_URL}/segments/#{segment_id}/subscribers")
+      uri = URI("#{MAILERLITE_API_URL}/segments/#{segment_id}/subscribers")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -56,7 +56,7 @@ def get_subscribers(segment_id:, filter: {}, limit: nil, after: nil)
     # @param segment_id [String] the ID of the Segments to delete
     # @return [HTTP::Response] the response from the API
     def delete(segment_id)
-      client.http.delete("#{API_URL}/segments/#{segment_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/segments/#{segment_id}")
     end
   end
 end
diff --git a/lib/mailerlite/subscribers/subscribers.rb b/lib/mailerlite/subscribers/subscribers.rb
index b3bad1d..239b187 100644
--- a/lib/mailerlite/subscribers/subscribers.rb
+++ b/lib/mailerlite/subscribers/subscribers.rb
@@ -23,7 +23,7 @@ def fetch(filter:, limit: nil, page: nil)
 
       params['limit'] = limit if limit
       params['page'] = page if page
-      uri = URI("#{API_URL}/subscribers")
+      uri = URI("#{MAILERLITE_API_URL}/subscribers")
       uri.query = URI.encode_www_form(params.compact)
       client.http.get(uri)
     end
@@ -52,7 +52,7 @@ def create(email:, fields: nil, groups: nil, status: nil, subscribed_at: nil, ip
       params['optin_ip'] = optin_ip if optin_ip
       params['unsubscribed_at'] = unsubscribed_at if unsubscribed_at
 
-      client.http.post("#{API_URL}/subscribers", json: params.compact)
+      client.http.post("#{MAILERLITE_API_URL}/subscribers", json: params.compact)
     end
 
     # Updates an existing subscriber with the specified details.
@@ -81,7 +81,7 @@ def update(subscriber_id, email: nil, fields: nil, groups: nil, status: nil, sub
       params['optin_ip'] = optin_ip if optin_ip
       params['unsubscribed_at'] = unsubscribed_at if unsubscribed_at
 
-      client.http.put("#{API_URL}/subscribers/#{subscriber_id}", json: params.compact)
+      client.http.put("#{MAILERLITE_API_URL}/subscribers/#{subscriber_id}", json: params.compact)
     end
 
     # Returns the details of the specified subscribers
@@ -89,7 +89,7 @@ def update(subscriber_id, email: nil, fields: nil, groups: nil, status: nil, sub
     # @param subscriber_id [String] the ID of the subscriber to get
     # @return [HTTP::Response] the response from the API
     def get(subscriber_id)
-      client.http.get("#{API_URL}/subscribers/#{subscriber_id}")
+      client.http.get("#{MAILERLITE_API_URL}/subscribers/#{subscriber_id}")
     end
 
     # Returns the details of the specified subscribers
@@ -97,14 +97,14 @@ def get(subscriber_id)
     # @param import_id [String] the ID of the import to fetch report
     # @return [HTTP::Response] the response from the API
     def get_single_import(import_id)
-      client.http.get("#{API_URL}/subscribers/import/#{import_id}")
+      client.http.get("#{MAILERLITE_API_URL}/subscribers/import/#{import_id}")
     end
 
     # Returns the total number of subscribers in the MailerLite account.
     #
     # @return [HTTP::Response] the response from the API
     def fetch_count
-      client.http.get("#{API_URL}/subscribers/?limit=0")
+      client.http.get("#{MAILERLITE_API_URL}/subscribers/?limit=0")
     end
 
     # Deletes the specified subscriber.
@@ -112,7 +112,7 @@ def fetch_count
     # @param subscriber_id [String] the ID of the subscriber to delete
     # @return [HTTP::Response] the response from the API
     def delete(subscriber_id)
-      client.http.delete("#{API_URL}/subscribers/#{subscriber_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/subscribers/#{subscriber_id}")
     end
 
     # Forgets the specified subscriber.
@@ -120,7 +120,7 @@ def delete(subscriber_id)
     # @param subscriber_id [String] the ID of the subscriber to forget
     # @return [HTTP::Response] the response from the API
     def forget(subscriber_id)
-      client.http.post("#{API_URL}/subscribers/#{subscriber_id}/forget")
+      client.http.post("#{MAILERLITE_API_URL}/subscribers/#{subscriber_id}/forget")
     end
   end
 end
diff --git a/lib/mailerlite/timezones/timezones.rb b/lib/mailerlite/timezones/timezones.rb
index 966e4c2..26da3f5 100644
--- a/lib/mailerlite/timezones/timezones.rb
+++ b/lib/mailerlite/timezones/timezones.rb
@@ -16,7 +16,7 @@ def initialize(client: MailerLite::Client.new)
     #
     # @return [HTTP::Response] the response from the API
     def list
-      client.http.get("#{API_URL}/timezones")
+      client.http.get("#{MAILERLITE_API_URL}/timezones")
     end
   end
 end
diff --git a/lib/mailerlite/webhooks/webhooks.rb b/lib/mailerlite/webhooks/webhooks.rb
index 6310c35..d963a90 100644
--- a/lib/mailerlite/webhooks/webhooks.rb
+++ b/lib/mailerlite/webhooks/webhooks.rb
@@ -16,7 +16,7 @@ def initialize(client: MailerLite::Client.new)
     #
     # @return [HTTP::Response] the response from the API
     def list
-      client.http.get("#{API_URL}/webhooks")
+      client.http.get("#{MAILERLITE_API_URL}/webhooks")
     end
 
     # Returns the details of the specified webhooks
@@ -24,7 +24,7 @@ def list
     # @param webhook_id [String] the ID of the webhooks to fetch
     # @return [HTTP::Response] the response from the API
     def get(webhook_id)
-      client.http.get("#{API_URL}/webhooks/#{webhook_id}")
+      client.http.get("#{MAILERLITE_API_URL}/webhooks/#{webhook_id}")
     end
 
     # Create a Webhook
@@ -36,7 +36,7 @@ def get(webhook_id)
     def create(events:, url:, name: nil)
       params = { 'events' => events, 'url' => url }
       params['name'] = name if name
-      client.http.post("#{API_URL}/webhooks", json: params.compact)
+      client.http.post("#{MAILERLITE_API_URL}/webhooks", json: params.compact)
     end
 
     # Update the specified Webhook
@@ -53,7 +53,7 @@ def update(webhook_id:, events: nil, name: nil, url: nil, enabled: nil)
       params['name'] = name if name
       params['url'] = url if url
       params['enabled'] = enabled if enabled
-      client.http.put("#{API_URL}/webhooks/#{webhook_id}", json: params.compact)
+      client.http.put("#{MAILERLITE_API_URL}/webhooks/#{webhook_id}", json: params.compact)
     end
 
     # Deletes the specified Webhook.
@@ -61,7 +61,7 @@ def update(webhook_id:, events: nil, name: nil, url: nil, enabled: nil)
     # @param webhook_id [String] the ID of the Webhook to delete
     # @return [HTTP::Response] the response from the API
     def delete(webhook_id)
-      client.http.delete("#{API_URL}/webhooks/#{webhook_id}")
+      client.http.delete("#{MAILERLITE_API_URL}/webhooks/#{webhook_id}")
     end
   end
 end