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?

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?