Authentication error 10000 when uploading image


The image upload via api.cloudflare,com suddenly stopped working again after not even a week. No one has changed anything in the meantime, API Token is still valid.

This command
curl -X POST "<accountID>/images/v1" -H "Authorization: Bearer <secret BAERER>" -F file=@"<an image>"
{"success":false,"errors":[{"code":10000,"message":"Authentication error"}]}

What is the exact problem and how to solve it without generating a new API Token a few times a month?