Good morning! When you're using credits it's a bit different now. If you have a credit note outstanding on a vendor, to use it you would choose what expense you are using it for (or G/L account or invoice you want to adjust it against) on the line in the 1st red box, and then at the bottom right, above total, you'll see a Credit box. In there type in how much of the credit you wish to use.
Hope that helps!
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