A nation doesn't issue bonds to cover the cost of its spending, but to remove money from circulation. It's simply a way of saying "hey, there's too much money around. If you let us remove some of it now, we'll give you back more in the future"

There's literally no situation where a sovereign nation would not be able to pay out the bonds it has issued. It's simply a matter of making the money printer go "brrrrr" and presto - the debt has been resolved

In the most broad terms, the only difference between realising bonds and simply printing the money is the lag time

As you say yourself - there is no magic

In the case of Zimbabwe, and as stated very well by imtringued in the other post to this thread, Zimbabwe could have invested in production, education, and infrastructure to grow the economy, instead of trying to sell bonds, which is essentially saying

"Hey, you know this currency that is rapidly loosing value - we're going to print so much more of it in the future! Doesn't this seem like a great investment?"