Yes. On Settle up, tap the amount and type what you're paying now. NEXO shows "Partial · ₱X will remain", records the payment, and the rest stays on the balance for next time.
Example: Sam owes Alex ₱2,000 and pays ₱500 today. Record ₱500. The Balances card then shows Sam owes Alex ₱1,500.
The only rule is that the amount must be more than zero.