GitLab takes into account the whitespace before and after the / . On the Repositories page (Organization Settings >> Repositories), you'll notice a space e.g. Owner / Repo (as opposed to Owner/Repo), which will need to be included in any command you're running.
If you are using GitLab's environment variables (https://docs.gitlab.com/ee/ci/variables/#debug-tracing) to pass the repository as CI_PROJECT_PATH in a cURL request for example, it may not include the spaces and you'll need to hardcode the name in order for it to work.