Reporter user cannot create merge request

Hi there!
We’ve just started using Gitlab and it’s great. But we had an issue with our reporter users, they can’t create a merge request. According to documentation ( they could create merge request without any special permission.
We are working with 3 main branches: development, testing and master. Each branch represents a specific environment and they all are configured the same way, nobody can make a direct push and only maintainers are allowed to merge. With the exception of branch development where developers also are allowed to merge.
Has our configuration an error or are we missing something?