Example: Whitening costs £500. The finance company are paying £450 towards the treatment and the other £50 is interest/practice are paying.

Go to Configure - Patient Payments and add in a payment type called 'Finance/0% Finance/etc'
Also tick 'Percentage Discounts'
Go to a patient, and chart the treatment as it should cost, eg the full £500. Invoice through as necessary but take no payments.
When the money comes in from the finance company, go to the patients' payment screen, and process the payment.
Enter in £450 and the payment method as 'Finance/0% Finance/etc', and enter £50 in the discount box, and a reason, eg Interest/Finance.
Click Process, and it will make the patients' balance nil, but will show that £500 was invoiced, £450 paid, and where and how the extra £50 was accounted for.

OR

You may wish to enter the finance payment before the treatment is completed and therefore an invoice may not be present. This will mean an error will appear if trying to add a discount as there is no invoice to discount.
In this instance, add the finance payment in full WITHOUT a discount added.
Now Add an adjustment and create a new adjustment type called FINANCE and set as per the below image:

You can then set the adjustment amount as what the discount would have been to apply this.

The following will only work if the INV_DISCNT adjustment type is set for a positive entry to DECREASE the amount

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