@JohnRo
You need to copy the value of box 2a or box 1 into box 16. That fixes it.
There's been some contention over whether it should be box 2a or box 1 that is used in box 16, but if they are the same value, it makes no difference.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*