Validate an EIN application request
⚠️ Early access — This endpoint is in preview and may change in backwards-incompatible ways before it is marked stable. Avoid depending on it in production, and reach out before building on it.
Check an EIN application payload for field-shape errors without creating a filing — the same dry-run pre-flight the formation validate endpoints offer. Returns every field error in one pass, including the conditional principal_activity follow-ups for the selected category.
This checks request-field shape only. The business existence check and the responsible-party vault requirements run on the create endpoint, so a payload that passes here can still be rejected when you submit it.

