You have invoiced a customer for product and later find that the selling price is incorrect. You can either advise the customer to "pay the invoice short" or you can provide the customer with a price credit. The first option has no documentation and you must later adjust off the short payment when you process the Customer Payment. The more precise process would be to issue a credit document so that both the customer and your company have a record of the transaction.
If the Sales Invoice has NOT been posted, you can simply edit the Price value on the invoice. Then reprint and post. Note that you can change ONLY the Price on an unposted Invoice. You cannot change a quantity, delete or add a line.
If the Sales Invoice is posted, follow this steps to generate a price credit.
1) Access Trans - Sales - Authorize Customer Unreturn Merchandise.
Click New, select the Customer, and then input the invoice number into the Sales Invoice field.
The line grid will populate with the lines from that invoice. Use Column Chooser so that grid includes "Quantity On Invoice", "Quantity", "Price", "Extended Price", and "Taxable". The Quantity On Invoice and Taxable values will default to that of the original invoice.
Toggle the checkmark column for the line(s) needing a price credit. The Quantity field will default to the same value as the Quantity On Invoice. In the Price field, input the Unit Price Difference you wish to give credit for. Example: If the original invoice was for 2 ea at $50.00 ea, and the price should have been $45 ea, this line should be input as Quantity = 2 and Price = $5 with Extended Price = $10. You can add any verbiage you like into the Notes field.
Click the Finalize button from the menu bar. This will create a Customer Credit.
2) You may print/email the credit directly from the Customer Credit screen (Trans - Sales - Customer Credit), or the credit will print out as part of the Sales Invoice Printing process.
3) The credit will also be included in the Sales Invoice Post process.
4) The customer now has a Customer Credit on their account. If this is an "open terms" account, you can either apply the credit towards the original invoice immediately, or you can elect to await the customer the submit their payment and you can apply the credit at that time. If the customer had already paid the original invoice or the invoice had been paid via credit card at time of sale, you can use the Customer Refund process to generate a Refund Check to the customer or generate a Credit Card Refund.