Error Page Appears When Signing In to DCS

Summary:

Self-Service users and Account Administrator users cannot sign in to DCS; 403 Forbidden error occurs.

Content (please ensure you mask any confidential information):

I implemented DCS following the “Implementing Digital Customer Service” guide and staged it with almost no changes from the template(25C).

• Sign-up works successfully.
• Self-Service users and Account Administrator users see a “Forbidden error – The server understood the request but refused to authorize it” page upon signing in, with the navigation menu briefly flashing just before the redirect.
• Developer tools show that accessing the mySelfServiceRoles endpoint returns a 403 Forbidden error.

I have contacted My Oracle Cloud Support, but no resolution has been provided for nearly a month.