Thanks Critter-3. Right, I was aware that I needed to pay income tax on the grant, but self-employment tax never even occurred to me - stupid me! User rjs helped me to understand that I should have included the grant money on my Schedule C as other business income that was not reported on a 1099-NEC or 1099-MISC, rather than as "Other 1099-G Income" on Schedule 1.
Thanks again for your help!
