Self-Employment Income and 1099?

Hi, 

 

I have a question and especially in consideration of like this time of year (Dec 30th and 31st). Its my understanding that one reports income based on when they receive it. 

 

This is where the rub question comes in. I know somebody that submitted an invoice payment like on the Dec 30th. But it takes a days to get to me FI. So, I am not going to receive that payment in my account until like the 2nd. 

So, how will this work? They are going to report a 1099 based on the amount they submitted for payment. Yet, I would report the income I received in up until Dec 31 based on what I received. So, there would be a difference based on what they submitted I haven't received.  How is this dealt with?