If you go on the following link you will receive the 502 error
502 Bad Gateway
https://hg.tryton.org/modules/notification_email/file/tip/tryton.cfg
hope it helps
regards
Matteo
It was because we still use mercurial with Python2 and the Gentoo distribution removed the support of pygments for it. I installed it with pip2 for the hg user.
It is really time to fix Issue 9158: Replace mercurial-server by hg-ssh - Tryton issue tracker.