The extra is kept as a deposit: credit toward future shared expenses.
Example: Sam owes Alex ₱800 and sends ₱1,000. NEXO shows "₱200 more than owed — held as a deposit". After recording it, the balance flips: Alex now owes Sam ₱200, which gets used up by Sam's share of the next shared expenses.
If the person paying doesn't owe anything, the whole payment is recorded as a deposit. The note on the record says so, for example "Settled up · GCash · incl. ₱200 deposit".