Help with a journal entry please

You would not do this with a journal entry because Accounts Receivable is impacted. Instead you record the discount when the receipt is posted. First under Maintain>>Customer defaults make sure that you have specified an Income account for posting Sales Discounts. This can be the same as your Sales/Income account or it can be a different account. Management choice. Then when the sale is made record the Invoice for the full UNdiscounted amount. Then when the customer pays their amount use the Receipt Task to record the amount paid as well as the Discount amount. There is a column for the discount.

Alternatively you could include the discount on the invoice as a credit but you will need to post it to the appropriate Income account as discussed above. Then all that is left on the customer account is the amount that they owe once the discount coupon is applied.