I have a 64-bit C# application running on Windows 10/11 that is making a successul initial request for the Authentication access_token. The URL for this request (and subsequent refresh) is https://api.refinitiv.com:443/auth/oauth2/v1/token. This access_token is successfully used in the WebSocket LogIn. After a prescribed interval (less than the "expires_in" seconds), the s/w requests a refresh of the access_token. The response sometimes is "OK", but unfortunately, many times the response is HTTP Status BadRequest RECEIVED: { "error": "invalid_grant"}. With this failure, the WebSocket disconnects. There can be upto six (6) successfult sequential "OK" refresh cycles, but out of the blue, there is arrives a failure.
Can anyone suggest the cause of the Authentication access_token refresh failure?