"Configured Username Attribute is not found in the provider response" error from JIRA REST API

[Deleted user]

I have begun getting this error from our JIRA REST API, and I'm not sure what it means, or how to fix.  (I can't find references to it on here, Stackoverflow, or anywhere else):

Configured Username Attribute is not found in the provider response

Could anyone advise?  (This is happening for all REST calls, and these were working a few days ago...)

[Ken McClean]

What's an example of an API endpoint you're using? What code are you using to reach it?

[Deleted user]

All endpoints are suddenly receiving this error -- even just a basic GET to query an individual issue:

/rest/api/2/issue/

The application is running in Python, but I get the same results even just testing via Postman

[Ken McClean]

Sounds like you're either not providing the username attribute that Jira is expecting, or the username you're using is invalid/inactive.

It's possible that the token you're using to authenticate has expired, and that this is just a misleading error message.

[Deleted user]

The ID is correct - and, actually, I'm able to manually log in to the UI with these credentials.   And I'm pulling a fresh token each time I test.  (And this also was working fine until last week).  Just not sure what may have changed that are bringing on this error, and what, specifically, this error really means.