I've faced with the following issue while using ctrf slack reporter:
Error: Failed to send Slack message: An HTTP protocol error occurred: statusCode = 400
Error: Process completed with exit code 1.
It would be much more user-friendly if we provide error details in console output for bad request

In my case i've faced that i put too long String into text area. I was using npx slack-ctrf custom with .hbs template.