Specify behaviour, not just screens.
Define the records and fields, who can see or change them, the workflow and reports, and what should happen when something goes wrong. Review these alongside the screens so permissions and operational behaviour are part of the design.
Treat integrations as a two-sided agreement.
Confirm the external provider's capabilities and access rights. Define data ownership, mappings, timing, duplicate handling, retries and reconciliation. A successful API response is not always proof that the business task is complete.
Useful questions, answered.
Review its source, licence, dependencies and current behaviour before deciding the change.
Yes, discuss the requirement through that route. Compatibility and delivery must still be agreed for the particular request.