When creating a custom SAML 2.0 integration for GitLab, the following error message is displayed by GitLab upon login:

Could not authenticate you from SAML because "Invalid audience. the audience [[Enter Audience URI]], did not match the expected audience [[Enter Audience URI]].

• GitLab
• Security Assertion Markup Language (SAML)

This is caused by the Audience URI (SP Entity ID), also known as the 'Issuer ID', on the Okta side not matching what is listed on the GitLab side.

Navigate to the GitLab Admin console and retrieve the GitLab provided Audience URI. Copy this value and navigate back to the Okta Admin console. Then, paste the value into the Audience URI (SP's Entity ID) field, which can be found in the custom SAML application integration section under the General Tab in the SAML Settings.