[Treasury Prime docs]: reservations are product-specific. The account_number_reservation entitlement must be enabled or you get a 403 with You are not entitled to use this feature. Creating a reservation with an invalid account product ID returns 404. Mismatched account products at application time return 400 with account_number_reservation_id is not valid for the provided account_product_id, and reusing a reservation returns 400 with account_number_reservation_id already used. Reservations never expire and cannot be released, so pick the right product before reserving.

Context: Account number reservations fail with 403 entitlement errors, 400 product mismatch errors, or 404 on invalid products.