If a mob boss owes you a favor, do you imagine that there is no debt because there is no fixed exchange rate between "a favor" and loaves of bread, or between favors and global production? You could argue that this isn't a debt for whatever reason, but if you ask a bunch of random people, I'm sure you'll find that pretty much everyone considers this to be "debt".*
It is a very good example because again it explains the difference between debt and property !
On the other hand, if I just propose to give a false testimony, to win his sympathy, with the idea that one day, he will return the favor, then there is no debt. However, I own abstractly some of his sympathy. That could be an illusion on my part. I may have invested wrongly in what I think to be the sympathy of a mob boss, with the idea that one day, I might ask him a favor. But if on that day, he laughs in my face, then I just invested wrongly.
* You can define debt narrowly and declare everyone else to be wrong, but this is folly. Economics is ultimately the study of people. If you disregard them, you are just jerking yourself off.