GET /accounts/missing-external-ids
Returns accounts that do not yet have an externalId assigned. Use this as the first step in the initial ID backfill. Fetch the list, match records to your system by name or domain, then use Map External IDs to write the IDs back in bulk.
This endpoint does not support
lastSync or cursor-based pagination. Only limit is accepted. The response is a plain array with no pagination wrapper.data