Inquiry About "User credentials have expired"

Dear Taboola support team.

Yesterday I did oauth authentication and got a refresh_token.
I used it to access the
I accessed the following endpoint
https://backstage.taboola.com/backstage/oauth/token

Then I got the error "User credentials have expired".

I tested with a different refresh_token and got the correct access_token, so I think the client_id is correct.

What are the possible reasons for the "User credentials have expired" error?
I understand that after a year, I need to authenticate oauth again, but since I just authenticated oauth yesterday, I don't know why.

Thank you in advance for your help.