The error message you're encountering from the Facebook Lead Ad API is as follows: "Unsupported get request. Object with ID 'xxxxxxxxxxxxxxxxx' does not exist, cannot be loaded due to missing permissions, or does not support this operation. Please refer to the Graph API documentation at
https://developers.facebook.com/docs/graph-api."
This message suggests that there may be an issue with the requested object's ID, insufficient permissions, or the operation not being supported. You can refer to the Graph API documentation for further guidance.
Please check the following thread on your concern and make sure that the Facebook account you have connected with the trigger event has ownership of the lead ad form means you need to be the admin of that Facebook lead and have to grant all the permission to access the Lead ad form. You can try making a new connection for your Facebook Lead ad and make sure you have granted all the permission of the respected page.