That's not what I mean by debt. If you violate the terms of trade, you can be sued. That court can then impose damages. Those damages will be in fiat currency, not strawberries, not bitcoin. Those damages will probably be more than the original price though, maybe even a lot more. However, the court may force you to pay in bitcoin or strawberries if they are aware that you hold such. If you claim you don't have any strawberries/bitcoin, then you'll be paying in fiat.