For reconciliation purposes, you’ll need to record each of the transactions involved, Pelita.

Below are the steps that suit perfectly for your scenario:

First, create a bill for $80. 

1. Click Vendors at the top. 
2. Select Enter Bills. 

Create a checque to pay the $80 bill. 

1. Open the $80 bill. 
2. Select Pay Bill at the top.  
3. Make sure to enter $100 on the AMT.TO PAY 
4. Enter Check on the Method. 
5. Click Pay Selected Bills.   

This should leave the vendor with a credit of $20. You can then create a deposit for $20 under Accounts Payable. Here’s how:

1. Click Banking at the top then select.
2. Select Make Deposit. 
3. Select the bank account on Deposit to. 
4. Enter the Vendor's name on Received From. 
5. Select Accounts Payable under From Account. 
6. Enter amount and other information. 
7. Click Save & Close. 

Setting the deposit to Accounts Payable will removed the $20 credit from the vendor's profile. This will also credit the amount back to the bank account. 

Please drop by again if there's anything else you need.