Rails / Action Text + Active Storage / Spaces

I am unable to upload files into DO Spaces that are uploaded via the Action Text editor. I can store them locally but not in Spaces.

I get the following message:

<Error>
<Code>SignatureDoesNotMatch</Code>
<RequestId>tx000000000000023fa55dc-005f037300-ab90b1-ams3b</RequestId>
<HostId>ab90b1-ams3b-ams3-zg02</HostId>
</Error>

I’m working locally - which suggests it can not be a CORS issue.

I can save files locally - which suggests the “web site” code is functional.

Here is a copy of the spaces configuration from storage.yml

spaces:
  service: 'S3'
  access_key_id: 'XXXXXXXX'
  secret_access_key: 'XXXXXXXX'
  region: 'ams3'
  bucket: 'at-development'
  endpoint: 'https://ams3.digitaloceanspaces.com'

I’m stuck. Any ideas where I should look?

Thanks - in advance.