I identified the cause of the Azure Synapse pipeline trigger error. After hours of troubleshooting and adjusting both SFDC and MS Azure Synapse instances, I discovered that an empty space ' ' character caused the issue at the beginning of the SFDC URL endpoint domain. I was trimming and regenerating the application client ID and secret, but I overlooked checking the URL. Once I found and removed the space from the endpoint, the Synapse Trigger ran successfully. My advice to anyone facing the same error is to make sure that the SFDC URL, Client ID, and Client Secret do not contain any extra characters.