LinuxGSM: Discord alerts failing for ut99server

When I use test-alert to check Discord alert functionality, I get this: [ FAIL ] Alert ut99-server: Sending Discord alert: {"code": 50006, "message": "Cannot send an empty message"}

I followed the instructions at https://github.com/GameServerManagers/LinuxGSM/wiki/Discord to create the Webhook and updated the server script to enable Discord alerts, but it’s not working as expected.

Any ideas?