Also, here is an example of 'looks simple' but 'raises many question'

1/ Should it be a discount on future invoices, or a refund (an angry customer will ask for a real refund: aka $$ on their bank account)?

2/ Do you want to keep track of how much has been discounted/refunded to which customer (so that you can identify deeper trends: if a segment is being discounted many times: maybe you can adjust things, or maybe it's fraud?)? In that case, just erasing a line doesn't help

3/ If you refund, how do you deal with taxes that have been paid already?

Btw, we've written a quick primer on Refunds, Coupons, and Credit Notes: to lay out the pros/cons

https://github.com/getlago/lago/wiki/A-Primer-on-Refunds,-Co...