Can not clone Repository via SSH from gitlab

I have logged in to my own hosted gitlab and try to download / install a dependency in a boss test project

But when I try to add the repository in the format:

boss install git@mygitlab.domain.de:delphi/libraries/mylib.git

I get the following error:

[INFO ] Installing modules in project path
[INFO ] Building cache files...
[INFO ] Updating cache of dependency gtrlib
[INFO ] Downloading dependency git@mygitlab.domain.de:delphi/libraries/mylib
[ERROR]   Cloning into 'X:\git_local\bosstest\modules\mylib'...
[ERROR]   fatal: unable to access 'https://mygitlab.domain.de:delphi/libraries/mylib/': URL rejected: Port number was not a decimal number between 0 and 65535
[ERROR] exit status 128

Why does it try to map the given repository path to a https:// path?
Is there another syntax on how to pass wht git@xxx/bla.git repository format?

Cloning the repositories manually on the command line using git directly works like a charm using ssh

Start by reproducing the reported boss install git@mygitlab.domain.de:delphi/libraries/mylib.git command and inspect how the dependency URL is handled before Git is invoked. Done means the SSH repository form is accepted and cloned without being rewritten into the malformed HTTPS URL shown in the error.