How do i apply the discount a customer has taken off their payment?

Hi swrenn-islandtru,

Welcome to Community!  Having options to record payments received by your customers is key in keeping your books balanced.  QuickBooks Online provides two choices for recording underpayments and overpayments.  I'd be happy to provide more information so you're on the right track with your QuickBooks goals!

Two options for recording this type of transaction are Discounts, or Journal Entries.  Here's a helpful guide for your reference.  However, before getting started, I recommend speaking with an accounting professional for the best course of action.  If you don't have an accountant, we can help you locate a ProAdvisor in your local area.

Feel free to reach back out with other questions.  We'd be glad to help!