Reference number for the transaction.
This is the reference number assigned to a transaction. Depending on the type of transaction, it appears in the QuickBooks user interface as Bill Number, Invoice Number, etc.
Reference numbers are alphanumeric strings and are not limited to actually being numbers.
For some types of transactions, if RefNumber is not assigned, QuickBooks will automatically assign a unique one. Reference numbers should generally be unique, but are not guaranteed to be so. It is recommended that applications generating their own reference numbers take steps to ensure their uniqueness.