How to debug failing webhook (plesk/wordpress)

Plesk/wordpress webhook authentication error

I’m trying to get simple push webhook to work w/ (hosted) plesk/wordpress setup. I have the ssh key in ‘deploy keys’, I can pull from the repo with ‘Pull Updates’ button in plesk, however when I test the webhook, it times out after 10.0x seconds. The only clue is

[2021-01-14 16:36:48.061] ERR [panel] Task failed: id=570, pid=11395, type=ext-git-task\create, error=fatal: Authentication failed for 'https://gitlab.com/RE/DAC/TED.git/'
[2021-01-14 16:36:48.061] ERR [panel] fatal: Authentication failed for 'https://gitlab.com/RE/DAC/TED.git/'

on the plesk side.

This happens with the SSL option on or off, and with hook URL on https or http. Our project is private, that shouldn’t be a problem?

Any suggestions on where to look next?