? how does one pay for a good, without money?

Well, as of right now, the only way to pay for a good is to pay for it with another good or service. As before, money is merely the accounting of debt. It only signifies a promise to provide a good or service in the future. You aren't really paying for something with money, you are delaying payment with a promise to actually pay later.

Given that, why do you think debt is necessary in the hypothetical future situation that was presented?

Because of how society works? Because currency is even more inherent to society than literacy?

That's how a society that needs (delayed) trade between people works, but the setting was a hypothetical future where a magical AI exists, that can provide for someone without needing to rely on other people.

Did you, uh, forget to read the thread?