[SL] How to apply a discount/credit given to a supplier order?

[<sql...@li...>]

I used to order from a this provider some products through a previous
company account I had with them.

I created a new entity and informed the supplier of this. Instead of
them making me a new account on their end, they just renamed my old one
to keep the history and such.

However in the previous company I had requested I get issued some credit
for some items that arrived bad. They apparently did a whole inspection
that took a while perhaps to get refunded from the manufacturer
themselves. I had totally forgotten about this credit honestly.

The other day I place an order and the representative told me he finally
applied that credit he owed me on my current order invoice.

So now I am not sure how to input this in SL because it really isn't
directly related to my new company.

Should I do a GL transaction to adjust?

For example the supplier invoice reads $200, but after the credit it's
$150. So I do not just want put the cost of the items to be actually
less when I create a vendor invoice, since that would just throw my
profit off by a bit. 

What is the correct way to adjust this accordingly? If its a GL
transaction, would I do this backward than traditional? 
ie. debit my bank account and credit the account for this item?

If someone can suggest something I would appreciate it.