The following error is dispalyed.

The App (Application) ID deletion is an external operation. An API call is used to delete App ID from the Azure server. The API calls are done over the network and sometimes due to network issues, timeouts or an error in the Azure servers, this Application Id is not deleted. In some scenarios, the Application Id is deleted but the return code fails from the API call.
You must manually delete the App from the Azure portal.
To delete the App:
You must have permissions to manage the Azure Active Directory (update/delete permissions)
2. On the Azure portal, click Azure Active Directory > App Registrations.
3. Enter the App ID in the search bar.
Note: The App ID given in the error message is usually in the form of a GUID. For example, bd2ddc9d-3528-4470-a4d3-597838f601dc
4. Open the App ID and click Delete.
The following screenshot displays the steps to be performed.

Backup Exec does not support removal of the Application Id manually from the Azure portal without trying to first remove the configuration from Backup Exec. It is recommended to remove the configuration from Backup Exec and if that fails, remove the Application ID from Azure.