So a simple B2 test…
D:\Documents\letters>duplicacy.exe init 123_docx2 b2://homer-media
Enter Backblaze account or application id:xxxxxxxxxxxxxxx
Enter corresponding Backblaze application key:yyyyyyyyyyyyyy
download URL is: https://f002.backblazeb2.com
Then nothing… no transfer…
Authentication must be working, as if I deliberately mis-enter the application key, I get an authentication warning.