Discrepancy between 1099 and income

Dear Experts,

 

I am self employed and file my returns as a sole proprietor. I got my 1099 for 2021 on Jan 1, 2022, say, with a total of $10,000. But I did not receive the last $1000 until Jan 5, 2022, i.e., I only got $9,000 in 2021. How should I resolve this discrepancy? It's 10% of my income so it makes a big difference.

 

Many thanks in advance!!

 

P.S. Just in case, the answers given at The 1099 forms overstate the year's income do not seem to answer my question.