Oracle AR payment terms with discount R12

Hello

I did an course on AR, but this is still not clear to me,

sorry maybe for the silly question ...

If you setup a payment term with a % discount , eg 10 % discount if the customer pays within 10 days, otherwise 30 days (due date)

--> if the customer receives an invoice of 100, he pays early so he would get this discount

but what happens in real live, the customer only pays 90 , or pays 100 and receives a credit note ?

or if he pays 90 , the open invoice amount is still 100 in AR , so in AR we need to do an adjustment ?

or is this all automagically automatically happening ?