I'm unable to add a GIT repo to my project

There can be several reasons for not being able to add a GIT repo to your project.  One of the less common reasons for failure to add a GIT is that you may be trying to add a GIT repo whose URI is not in the form

git@<your.git-server.com>  

Some GIT servers are setup to use a username that is not 'git', so the URI would look like

<your-user>@<your.git-server.com>

At the moment this is not supported by Domino and a repo that has a URI with a non 'git' user cannot be added directly to a Domino project.  

To work around this you will need to access your repo using standard git push/pull/fetch/commit commands from within your execution.  In a job this would be in your code and in a workspace these can be executed from the workspace terminal command line.  

We are looking in to adding this functionality in a future version of Domino, but as of Domino v5.2 this is the current situation.