I answered "The night will be paid for" and it was accepted - my interpretation is that the speaker is inviting another person out and is promising to pay all the expenses over the course of the night. (dinner, movie tickets, drinks, etc.)
Paga, pago, pagas, pagos are participle forms of the verb pagar. We also have pagado. For ser and estar use pago, for ter and haver use pagado. But nowadays many people use pago with any verb.it has number and gender, thats why A noite foi pagA.