namespaced-path-encoding

Official doc： https://docs.gitlab.com/ce/api/README.html#namespaced-path-encoding

If using namespaced API calls, make sure that the NAMESPACE/PROJECT_PATH is URL-encoded.

For example, / is represented by %2F:

GET /api/v4/projects/diaspora%2Fdiaspora

Solution

If you are using nginx as a proxy to access gitlab:

change proxy_pass from proxy_pass https://gitlab/ to proxy_pass proxy_pass https://gitlab$request_uri;