Hey there Greg,
Gitlab does in-fact support the use of git archive. I was able to do this successfully via SSH - example below.
git archive --remote git@gitlab.com:gitlab-org/distribution/team-tasks.git -o test.zip HEAD
The above example uses the public repo here. The format for your SSH connection should be as follows:
git@<hostname>:path/to/project.git
You can also clone the needed URL via the project directly, by clicking on the clone button in the top right and selecting the SSH URL.
Also, would you mind trying this out without the ‘:app/’ appended to the end? I’m not really sure what this is doing. It doesn’t look like this is something that is used often, the above information took a bit of time to find.