Hi @matt.groves,
Thanks a lot for this suggestion. For all intents and purposes, the url attribute is the full unique identifier for resources surfaced through the FreeAgent API as it contains all the information the API needs to understand what resource you’re requesting (for which environment, which type of resource such as contact, invoice, project etc, and which specific item of that type). My recommendation would be not to rely on the integer values in isolation as then you’d need to reconstruct the URL any time you need to access or refer to a particular resource, meaning your app would need to understand how to construct correct URLs for them.
Best wishes,
Ewa