How to Use Return Sales Invoice Credit

My example is:

1 - I made a sale for $140
2 - I received the $140
3 - Customer returned $70 worth of products
4 - I made another $150 sale, but I want to allocate the credit to that sale.
5 - The only way I found it is through the payment entry, however I am obliged to enter 0.01 in paid amout, for the reference table to appear.

I just wanted to allocate the return amount on the invoice to bill the rest of the customer.

but i cant do it, because “Paid Amout” must be setted, it’s a bug?