Send partial payments with money amount less than the amount specified on 2 conditions:
- Sender has less money than the aamount specified in the payment Tx.
- Sender has the tfPartialPayment flag activated.
Other ways to specify flags are by using Hex code and decimal code. eg. For partial payment(tfPartialPayment) decimal ->131072, hex -> 0x00020000
For more context, see Partial Payments