Some resources have two similarly-named fields. For example, issues, merge requests, and project milestones. The fields are:
- id: ID that is unique across all projects.
iid: additional, internal ID that is unique in the scope of a single project.
Note: The iid is displayed in the web UI. If a resource has the iid field and the id field, the iid field is usually used instead of id to fetch the resource.
For example, suppose a project with id: 42 has an issue with id: 46 and iid: 5. In this case:
A valid API call to retrieve the issue is GET /projects/42/issues/5
An invalid API call to retrieve the issue is GET /projects/42/issues/46.