I am a sole proprietor and did not have positive net income on Schedule C in 2022. But, I have taxable income on Schedule 1 (2a) of my 2022 return. Can I contribute to solo 401k? (I want to maximize my retirement contributions so input welcome.) Thanks.
No your solo 401k is tied to your self-employment income so you cannot contribute as part of your business retirement plan.
IRS Schedule C, Profit or Loss from Business, is a tax form you file with your Form 1040 to report income and expenses for your business. The resulting profit or loss is typically considered self-employment income.
Usually, if you fill out Schedule C you'll also have to fill out Schedule SE, "Self-Employment Tax." You'll use this form to calculate your Social Security and Medicare tax based on your self-employment income and report it on Form 1040, Schedule 2 Part II, Other Taxes.
Above explains or adds/supports what MaryK4 is trying to tell a NO to your question.
Hope this helps