The SIM guide provides the following information related to partial authorization:
Partial Authorization Transactions
A partial authorization, or split tender, order is one in which two or more transactions are used to cover the total amount of the order.
The merchant must indicate that they are able to handle the extra processing either by selecting the Partial Authorization option in the Account settings of the Merchant Interface, or by sending x_allow_partial_auth=true with each transaction. Without this flag, the transaction would be handled as any other, and would be either fully authorized or declined due to lack of funds on the card.
When the first transaction is successfully authorized for a partial amount of the order, a split tender ID is generated and returned in the response. This ID must be passed back with each of the remaining transactions of the group, using x_split_tender_id=<value>. If you include both a split tender ID and a transaction ID on the same request, an error results.
If successfully authorized, all transactions in the group are held until the final transaction of the group is successfully authorized, unless the merchant has indicated either by input parameter or default configuration that the transactions should not be held.
The following fields are returned in the relay response data sent to the merchant's URL. The data they represent are in all prepaid card responses.
•x_prepaid_requested_amount—this is the amount requested.
•x_split_tender_id—this is the Split Tender ID provided when the first partial authorization transaction was issued.
•x_split_tender_status—indicates whether or not the transaction is complete.
•x_card_type—the card type.
The response fields outlined above are relative to SIM Relay Response. The information provided does not relate to any connection in which the merchant is collecting the payment data on their own payment form, it specifically is referring to the SIM connection method which uses the Authorize.Net hosted payment form.This is why the guide states that a split tender ID is generated and returned in the response when the first transaction is authorized for a partial amount of the order total.
Thank you,
Elaine