The proposition that there is not enough money, because of interest, is flawed.
The system will crash because governments spend more than their income. The music stops when nobody wants to lend more.
Indeed, this has nothing to do with money. This has to do with the flows of goods and services. States essentially take goods and services from their citizens. Part of it, they take directly as taxes, but a part of it, they promise to give back, while they are actually consuming it, and have no way of giving it back, except taking it still elsewhere.