How do I record Over payment charges?

How do I record Over payment charges?

Hello,

I have a tour company, I charge my customer using a booking software. The software collects payments and I get paid the total of weekly sales once a week.

I record each sale individually in Zoho Books. When I get the deposit from the booking company I match each sale to the amount. This has worked great so far.

The problem I have is that sometimes the amount I get deposited into my account is less than the total of all sales, this could be due to a return, money back, over payment. It is extremely unpractical for me to check each transaction and check the cause for the difference in the amounts.

After matching all transactions I am left with a difference, I need to add an adjustment and a withdrawal with the difference. 

My question is: How would you categorize this transaction? It is not an expense since I am simply returning money I was overpaid.