It has to do with paying the self employment tax if you had a Net Profit on Schedule C.
The self employment tax deferral was an optional benefit. It is also a deferral rather than forgiveness, so those amounts will eventually need to be repaid. Half of the deferred amount is due on December 31, 2021, and the other half is due on December 31, 2022.
Check if you have a Schedule 3 line 12e which goes to 1040 line 31.
See this video on how to pay
How do I find out how much I owe in deferred taxes?