The parameters can be set only on second (and subsequent) builds).

Steps to reproduce :

• have a gitlab project with a Jenkinsfile that needs parameters (see https://jenkins.io/doc/book/pipeline/jenkinsfile/#handling-parameters)
• create a gitlab group that can scan this project (with no automatic build)
• go to the project page in the jenkins UI : there is a link "Start a build", that does what it says, without letting the user pass any parameters

Expected behavior : the link should be "Start a build with parameters", and should let the user give the parameters

Workaround : start a first build, and interrupt it after the git checkout. Then the link correctly becomes "Start a build with parameters"