1099C is a cancellation of debt form.

In the real world, they're used when someone holding the debt has decided to abandon it, TYPICALLY as part of some renegotiation. It's tax paperwork showing that the debt is gone (which is de facto income and so tax-relevant).

These types believe that you can file them unilaterally to get rid of a debt, because it says debt cancellation in the title and the the world is a vast and all-powerful conspiracy that also is vulnerable to uncountably many technical loopholes.

edit: or it's part of the weird belief that the government has a massive pool of money they hold that belongs to you, and if you just speak the right incantations by filing weird paperwork suddenly they'll use the secret bank account to pay off all your debts and free you of your contract/citizenship/slavery or whatever the fuck. Gets very weird very fast.

File Form 1099-C for each debtor for whom you canceled $600 or more of a debt owed to you if:

You are an applicable financial entity.
An identifiable event has occurred.

https://www.irs.gov/forms-pubs/about-form-1099-c