GitLab jenkins integration

Hello ,i have been trying to integrate between jenkins and gitlab with public projects it work ,but when i change the project to internal or private i get the next error
failed to connect to repository :command "git is remotre -h returned status code 128 :stdout stderr:error : The requested URL returned error :401 Unauthorized while accessing on jenkins

i can’t add any credentials when i press add and fill the fields nothing happens .

thanks .