Blocks a list of accounts, each with its own reason, comment, and external_reference.

Up to 1,000 entries per request; more returns 400 for the whole request. Otherwise it always returns 200, with one result per entry in the same order as the request: an invalid entry does not fail the others. If the same user_id appears twice, the entries are processed in order; the second changes nothing and gets the same result.

Safe to retry: if the account is already in that state, the entry gets the same result and the existing id (the same id), without side effects or a new history entry. A retry with different data (for example, another reason) does not change the account or the recorded reason.