Write an item to storage: "storage provider could not be found in turn state."

[dweeb1937]

I'd like to use Bot.Builder.Community.Components.Storage to write a specific piece of data as a blob to Azure blob storage. But when I install this package to Bot Framework Composer it throws the error "WriteStorageItem: storage provider could not be found in turn state."
I have tried the following in appsettings.json, under runtime settings:

 "blobStorage": {
        "connectionString": "DefaultEndpointsProtocol=https;AccountName=myaccountname;AccountKey=myaccountkey==;EndpointSuffix=core.windows.net",
        "container": "storage"
      },

and

      "BlobConnectionString": "DefaultEndpointsProtocol=https;AccountName=myaccountname;AccountKey=myaccountkey==;EndpointSuffix=core.windows.net",
      "BlobContainerName": "storage"

and

      "storage": "blobStorage",
      "telemetry": {
        "logActivities": true,
        "logPersonalInformation": false,
        "options": {
          "connectionString": "DefaultEndpointsProtocol=https;AccountName=myaccountname;AccountKey=myaccountkey==;EndpointSuffix=core.windows.net",
          "containerName": "storage"
        }
      },

But they all have this same error message. I note that adding the following there is successful in automatically storing blobs of bot state but doesn't allow me to construct and send a specific blob.
Any advice gratefully received.

      "blobTranscript": {
        "connectionString": "DefaultEndpointsProtocol=https;AccountName=myaccountname;AccountKey=myaccountkey==;EndpointSuffix=core.windows.net",
        "containerName": "transcripts"
      }

My BFC context is:

Version:  2.1.2
Electron: 8.2.4
Chrome: 80.0.3987.165
NodeJS: 12.13.0
V8: 8.0.426.27-electron.0