But why didn’t he pay the debt tho.

my theory is that it's not in taeju's control to cancel debt. he told euihyun that he'll cancel it as a sense of comfort to euihyun even tho he hasn't done it yet, but is sincere abt it and was trying to find ways to make it come true. that is until euihyun got kidnapped.

He was gonna make his dad suffer and pay it. Plus Tae ju definitely was panicking over what would happen if euhyun paid the debt and still didn't like him by the end. Lol

I seriously doubt he was gonna make euhyun pay it at all