I thought it’s not [possible] , but it is upon checking their iOS app. Take note, I didn’t only check it, but tried it, and it worked!
An account number is required to make a payment which is commonly present in a bill.
It is possible to pay just a partial amount of the outstanding bill. Not sure with the minimum though. Just enter the amount in the box provided.
Like other payment facilities, posting of payment made via GCash takes up to 2 business days.
No extra fee!