"I want to pay."
Translation:Saya mau membayar.
Actually there is a slight difference between the two words.
Mau = to want (with determination) Ingin = to want (hope, expectation)
I want to dream about you tonight = Saya ingin memimpikan kamu malam ini (expectation)
I want to marry you next month = Saya mau menikahi kamu bulan depan (determination). But if without specific time given, it's considered expectation. So the meaning change to "Saya ingin menikahi kamu"