Fatal: could not read Username for 'https://gitlab.com

I am trying to use gitlab webhook, my webbook works perfectly for public repo, but for a private repo its giving error
“Hook executed successfully but returned HTTP 500 === ERROR: Pull failed using GIT /usr/bin/git and DIR /var/www/html/app/ === fatal: could not read Username for ‘https://gitlab.com’: No such device or address HEAD is now at df699ba Add new file”

I already added public ssh key in my gitlab account, also if I try
ssh -T git@gitlab.com
It’s showing me a welcome message