Core answer
Start here. This is the direct spoken answer to practice first.
Why this question matters
A form can have solid backend validation and still feel broken if the frontend cannot explain the error. This drill checks the practical handoff between API error shape and user-facing recovery.
I would agree on an error response that separates field errors from general errors. Field errors use stable field keys that match the form model, and general errors appear near the submit action or in a summary. After a failed submit, the UI keeps the user's input, marks invalid fields, focuses the first meaningful error, and lets the user resubmit after corrections. Unknown errors fall back to a safe message.