Slack cloud hook failing in new VM


We have recently migrated to a new VM. Our Slack cloud hook is now failing to send any notifications. I have confirmed separately that the Slack webhook URL used is still correct and works when sending a POST request via curl on the VM.

When setting up in the Prefect UI, the cloud hook test fails with no error message (image attached). We are using Prefect v1.2.2.

Any help is appreciated!