Fail to send mails with custom provider

Hi.
Im using AWS SES as my custom emails provider.

For some reason, Auth0 receive the following error while trying to send emails:

The security token included in the request is invalid

now, I know that this issue is sometimes related to wrong AWS credentials… BUT, those credentials worked until now (about 1 month) just fine. Nothing has changed in auth0 nor AWS side (for example: the auth0 user permissions). the emails were sent until now…

In addition, I verified that I can send emails with aws-sdk with the same credentials and it worked fine…

What can be the problem?