GitLab Service Desk on Omnibus: Activation Checkbox not visible

Hi Community!

I have installed the latest GitLab CE update last week (13.2.1) and wanted to try out the Service Desk.
So i followed the instructions on https://docs.gitlab.com/ee/administration/incoming_email.html#set-it-up
and configured my gitlab.rb file.
After running a reconfigure, restart and
sudo gitlab-rake gitlab:incoming_email:check
everything seems fine and looks like in https://www.youtube.com/watch?v=PId7jlcAkqk&t=1m20s
Even the new item unter “Issues” appeared
However, if i go to project settings -> general -> service desk as a maintainer, i get the following message:

Thanks for your help in advance

Florian