How to Handle (Partial) Non-Payment on 1099-MISC

Yes,  you can claim the 20% as a business bad debt expense,  if your 1099-MISC form reported 100% of the billings.

No, you can't claim the money you never received and never reported as income, as a business bad debt expense if your 1099-MISC form reported 80% of the billings. 

To enter your business bad debt expense:

1. Log-on to your TurboTax.
2. Select Pick up where you left off.
3. On the left side menu, select Federal then Wages & Income.
4. On the Your income and expenses screen, scroll down to Self-employment income and expenses and Review.
5. Continue until you get to the Here's your XXX info screen. Scroll down to Add expenses for this work.
6. If you get to the First, select the expenses you know you had screen, select Other miscellaneous expenses and Continue then I'm done.
7. Back at the Here's your XXX info screen, scroll down to Other miscellaneous expenses and Start. 
8. On the Let's enter the miscellaneous expenses for your XXX work screen, enter a description and the amount. 
9. Continue with the onscreen interview until complete. 

Thank you Helen,

It seems strange that if they ignored the last invoice, both in the 1099 reporting and in paying it actually, then I'm just at a total loss, but I'll accept it for what it is.  (This was a small side gig anyway)