Responses

B'cuz seme-san kept his deal by not only by keeping uke-san's secret of embezzlement but by also providing the embezzled money from his side while the uke was completely unaware of it. So the seme has "PAID" his part of the deal and now it's the uke's turn to return the favor by offering himself as payment.
After 30 chapters we got to know why the manhwa was named Paid