401 missing authorization

Today I get a 401 missing authorization on a API call whereas till yesterday it was running fine, and no changes have been made.

I am not a coder, nor familiar with Yii, and this is an existing project done by someone not available anymore.
Where should I look; I looked at the app.log, hoping to understand what is going on, but no joy.

Thank you

Hi keneso, this question is far to open. But API authorizations keys could have an expiration date.

Probably its just a matter of regenerating the key.