CX Sales Deal Advisor Agent — 403 CLIENT_ERROR for specific roles only

Has anyone run into the Deal Advisor Agent failing for only certain roles?

Deal Advisor Agent configured in 26B via AI Agent Studio, smart action published and working for custom admin roles. For other custom non-admin roles, invoking the agent via opportunity Smart Action, the default prompt "Give me a brief overview of this opportunity" returns into error -

"Request failed with status 403 and error response family CLIENT_ERROR" (Refer below screenshot)

End users see: "Sorry, the assistant is unavailable right now. If the issue persists, contact your help desk."
The same prompt, however, results in appropriate results when tested for custom admin role.