Hello everyone, two questions

A)

How can I generate a surcharge to a client for not making the payment on time.

Total Invoice: $ 100

Invoice date: 10/20/2020

Invoice Due Date: 10/27/2020

Today is 10/30/2020

I need to evaluate these options

1) add $ 2 x day, so today you must pay $ 106

2) add 2%, then you must pay $ 102

B) How do I set the credit limit for a client?

Thanks