Have you created a clearing account, monahakb?

You'll want to make sure you create a clearing account first before you proceed to creating journal entries. Here's how:

1. Click Lists on the menu.
2. Select Chart of Accounts.
3. Right-click anywhere in the Chart of Accounts then choose New.
4. Once you are in the Add New Account window, choose Bank then select Continue.
5. In the Account Name field, you can put in Clearing Account, Barter Account, or Wash Account.
6. Leave the Opening Balance field blank, then select Save & Close

For a more detailed guide in creating clearing accounts, see Set up a clearing account.

Next step is to create a journal entry to move the credit from the customer to the clearing account:

1. Go to the Company menu, then select Make General Journal Entries.
2. On the first line, credit Accounts Payable with the amount to be transferred. In the Name column, select the vendor from whom the credit is coming.
3. On the second line, debit the Clearing account created in step 1 with the same amount.
4. Select Save & Close.

Third, apply the credit to the Journal Entry created as an unpaid invoice

1. From the Customers menu, select Customer Center. 
2. Create Invoice, then under Transactions Tab select Received Payments. 
3. From the transactions list, double click the payment.
4. Put a check mark on the journal entry. 
5. Click on Discount and Credits 
6. Hit Save and Close. 

Fourth, create a journal entry to move the credit from the clearing account to another customer: 

1. From the Company menu, select Make General Journal Entries. 
2. On the first line, credit the Accounts Receivable with the amount to be transferred. In the Name column, select the Customer name. CTRL+I to create an invoice. 
3. On the second line, Credit the Barter Account you created.  
4. Select Save and Close.

Lastly, apply the credit to the unpaid invoice of the other customer:

1. From the Customers menu, select Receive Payments. 
2. Select the Customer you are transferring the credits. 
3. Put a check mark on the appropriate invoice, then select Discounts & Credits.
4. Go to the Credits tab and select the credit(s) you wish to apply, then select Done. 
5. Click Save and Close.

By following these steps, you'll be able to transfer the credit to another customer. 

I'll be right here if you need further assistance.