diff --git a/livekit-api/livekit/api/_service.py b/livekit-api/livekit/api/_service.py
index 31527d00..2a1e0553 100644
--- a/livekit-api/livekit/api/_service.py
+++ b/livekit-api/livekit/api/_service.py
@@ -18,11 +18,13 @@ def __init__(
         self.api_secret = api_secret
 
     def _auth_header(
-        self, grants: VideoGrants, sip: SIPGrants | None = None
+        self, grants: VideoGrants | None, sip: SIPGrants | None = None
     ) -> Dict[str, str]:
-        tok = AccessToken(self.api_key, self.api_secret).with_grants(grants)
+        tok = AccessToken(self.api_key, self.api_secret)
+        if grants:
+            tok.with_grants(grants)
         if sip is not None:
-            tok = tok.with_sip_grants(sip)
+            tok.with_sip_grants(sip)
 
         token = tok.to_jwt()
 
diff --git a/livekit-api/livekit/api/sip_service.py b/livekit-api/livekit/api/sip_service.py
index 80810528..6d3f122e 100644
--- a/livekit-api/livekit/api/sip_service.py
+++ b/livekit-api/livekit/api/sip_service.py
@@ -132,3 +132,20 @@ async def create_sip_participant(
             self._auth_header(VideoGrants(), sip=SIPGrants(call=True)),
             proto_sip.SIPParticipantInfo,
         )
+
+    async def transfer_sip_participant(
+        self, transfer: proto_sip.TransferSIPParticipantRequest
+    ) -> proto_sip.SIPParticipantInfo:
+        return await self._client.request(
+            SVC,
+            "TransferSIPParticipant",
+            transfer,
+            self._auth_header(
+                VideoGrants(
+                    room_admin=True,
+                    room=transfer.room_name,
+                ),
+                sip=SIPGrants(call=True),
+            ),
+            proto_sip.SIPParticipantInfo,
+        )