@Rishabh Gambhir (Capgemini America Inc) Did you try to check if the REST API request using Entra ID works directly with OpenAI service? I believe a custom subdomain is required as per pre-reqs.
If it works directly and fails with the connector in power automate then probably the error might be from power automate flow and the tracking id needs to be looked up to check for more details.
REST API reference for OpenAI which mentions to use Authorization header with bearer token. Thanks!!