How do I trigger off an expense in Quickbooks?

A purchase object represents an expense, such as a purchase made from a vendor. Given this, the appropriate trigger to use in your recipe is the "New Purchase" event trigger.

Please take note that:

• You must specify an AccountRef for all purchases.
• The TotalAmtattribute must add up to sum of Line.Amount attributes.

There are three types of purchases: Cash, Check, and Credit Card.

• Cash Purchase contains information regarding a payment made in cash.
• Check Purchase contains information regarding a payment made by check.
• Credit Card Purchase contains information regarding a payment made by credit card or refunded/credited back to a credit card.

For example, to create a transaction that sends a check to a vendor, create a Purchase object with PaymentType set to Check.