I work for a small company but we got a new system. Last year there were payment
Received but not posted to there accounts. I verified this by requesting copies of checks.
What is the correct way to input them and not putting the payment into the checking accounting . But I guess still saying that the payment were received?

Can you just go back to your 2005 financial statements and made the adjusting entry and prepare new statements? That is, higher cash, lower AR?

Or, if that is such a huge issue, you can always just post it to 2006 if it is not a super material amount.

But if you can, just go back and adjust the 2005 numbers.