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 ''
[2021-01-14 16:36:48.061] ERR [panel] fatal: Authentication failed for ''

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?