We owe a customer 70.00 (purchase invoice) and he owes us 70.00 (sales invoice) he has asked that I allocate what we owe him to the sales invoice, how do I do this?

Hi KimE3, you can record this by entering a contra payment following the steps below: 

1. Select + New > Journal entry

2. For line 1, select Debtors (Accounts Receivable) in the Accounts column.
- Enter the credit amount in the Credits column. 
- Enter the name of the customer in the Name column. 
3. For line 2, select Creditors (Accounts payable) in the Accounts column.
- Enter the debit amount in the Debits column. 
- Enter the name of the supplier in the Name column.
4. To save the journal entry, click Save.
5. Open the outstanding invoice and select Receive payment. 
6. Use the journal to pay off the full outstanding balance and Save. 
7. Open the outstanding bill and click Make payment. 
8. Use the journal to settle the outstanding amount.