@Opus 17 wrote:
Having box 1 zero is not necessarily wrong
It's true that box 1 could be zero, but in the original question pencil123 said "I contributed all of my 2020 salary to Solo 401K..." So the S corp paid him, say $20,000, and he contributed the whole $20,000 to his 401(k), so box 1 is zero. But he also said he withheld $400 for federal income tax. Where did the $400 come from? There's no money left after the 401(k) contribution. I think Mike9241 is right. It doesn't work. Box 2 can't be more than box 1.
