Hello sonal khatri,
Thank you for contacting Microsoft Support!
This error is a generic server-side error indicating that something unexpected happened on the server, but it doesn’t provide specific details about what went wrong.
Here are some potential reasons for this issue:
- Server-Side Bugs: There might be bugs in the server code that handle the cancellation request, causing it to fail after completing the action.
- Timeouts: If the server takes too long to process the request, it might timeout and return a 500 error.
I tried to cancel an appointment using Graph API and cancelled successfully. Please check below.

After following all the steps and still facing issue, I would recommend you to raise a support case with Microsoft Graph, a Support Engineer will be able to look into this issue and assist you better. You can raise support ticket from New support request - Microsoft Entra admin center or https://admin.microsoft.com/#/support/requests.
Hope this helps.
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