I solved the problem. Nobody told me I had to create another application key. They are only good for one time use.

Please mark issue resolved.

I have Cloudberry Explorer for Amazon S3 build 5.9.3.5 . I open the program. I go to File | New S3 Compatible Account | Backblaze B2.

I get a panel Add New Backlaze B2 Account. This panel has these three fields: Display name (documentation says I can use any value here), Application key ID (Backblaze keyName), and Application key (Backblaze keyID).

I am not sure I have put these last two items into the correct fields, but I have tested both ways. Maybe the Backblaze keyID should appear in the Application key ID field, and the Backblaze keyID should be placed inn the Application key field.

I have two application ID "pairs." The first is the Master Application ID, and the info on the panel in the program says I should use the AccountID. I do not know what is the AccountID. I have read the caveat at the bottom of the web page that you referred me to, yet it is still unclear what I supposed to enter in which field. I have tried several combinations of values.

Either way, when I try using the Application Key that I have created, with the two fields as I have stated above AND with the two fields reversed, I still get the authentication error that I have referred to.

I also see bucketID, but I do not think that could have relevance to this problem.