Impossible to use NAMESPACE/PROJECT_NAME to call API (yes, URL-encoded)

curl -k --header "PRIVATE-TOKEN: ************" "http://gitlab-ee.hostname/api/v3/projects/1" return expected payload but

curl -k --header "PRIVATE-TOKEN: ************" "http://gitlab-ee.hostname/api/v3/projects/NAMESPACE%2FPROJECT_NAME" return {"message":"404 Project Not Found"}