Most of France's debt in 1789 was from rentes viagères - life annuities sold by the French government. You'd buy them, and get payments for the rest of your life. Many of these (especially from 1770 and onward,) were flat-rate annuities, so people bought them for their babies to get huge returns. The costs of this program were staggering, it was a horrible way for the government to raise money.

The banks of Geneva took major advantage of France's rentes viagères, by finding 5 - 10 year old girls (who wouldn't be drafted) from families with a history of longevity, who were also smallpox survivors. The money would of course go to the banks, not the girls. You were allowed to buy life annuities based on anyone's life, but you'd have to prove they were still alive each year.

France also raised money with perpetual debt. Most of these debts were rentes sur l'Hôtel de Ville de Paris - you'd buy one and get 5% interest forever, with the right to sell that collection right to others (but one year of interest would be skipped if you sold/transferred it.) Again, this is a horrible way to raise money because the government got paid once and then had to pay out interest forever (even after the buyer's death.) The rentes sur l'Hôtel de Ville de Paris were the most secure debt you could buy from France, because tax money first went towards paying that before the money went into the general royal funds.

France also sold shares to a company that made profits from France's colonies (such as Haiti and a very large piece of North America, which Napoleon would later sell off to the US government.) There were guaranteed, government-backed, high dividend payments that the shares paid out each year.

The French government also sold bonds, which were purchased by French banks and wealthy individuals.

France also issued many short-term "IOUs" to businesses that sold things to the government, and then sometimes converted those into long-term debt. By 1788, over 55% of France's annual budget went towards interest on its debt.

King Louis XVI promised that France would not default on its debt again. To do this, they were going to institute a land tax, with no exemptions for members of the wealthy landowner class. This was rejected by the Parlement (not Parliament) of Paris, which said it had to be a nation-wide decision. So he announced that that would happen in the Spring of 1789, and once that was about to happen (and in part because that was about to happen,) the French Revolution began and the king was executed.