This is how you would perform an invoice adjustment if you have integrated EFTPOS. You would need to make an adjustment when a customer has paid via integrated EFTPOS however the staff member has input the value incorrectly in ClickPOS.
eg. A product has sale price of $10, however staff member accidentally charged customer 10 cents. Due to customer paying via integrated EFTPOS an adjustment needs to be made.
First you need to create an Adjustment payment button. To do this proceed to Maintain > System Admin > Payment Type
In Add Payment screen, fill in highlighted fields below. Below screenshot is an example
Now you have successfully created your Adjustment button :)
Let's put it into practice using the above example
To make an adjustment you would search old sale via invoice number, there should still be $9.90 owing on the invoice. You would tender this with the Adjustment button.