Error Code 9 is a failed precondition, see more about the error codes here if interested.
I think the issue here is that your Customer Account ID in the create and delete don’t match. In your create the ID is QWNjb3VudDo2OTgxNg==, while in the delete the ID is QXBpV2ViaG9vazo2NDMzOTA4. They don’t decode to the same value either. I would suggest setting the value of the Customer Account ID in your webhook_delete mutation to QWNjb3VudDo2OTgxNg==
Please let me know if you have any questions or concerns.