This can happen if you provide two different types of authentication for the Step. There are two types:
Apple ID-based authentication: Your Apple ID, password, and if available, an app-specific password to authenticate.
API key authentication: An API key set up on App Store Connect.
Do NOT provide both an API key AND Apple ID-based authentication information at the same time. In the example below, you can see that only the API key-based authentication is used. The other authentication-related inputs are left empty.