Use externalRef when a Project in Relic also exists in another platform — for example a contract number, a job code from your accounting software, or an identifier from a partner agency's database. Storing that outside identifier on the Project lets you cross-reference the two systems without changing the Project's own name or projectPrefix. Because it is optional, you can leave it blank for projects that have no external counterpart. It is purely a reference value: it does not drive catalog numbering or uniqueness, so it is safe to fill in or update at any point in the project's life.
Technical section
Data model, API, and internals — visible to developers.