Ok, I see the issue. Do not renumber the item on the item card, but just re-select it on the Item Journal Line. You are doing everything else totally correct, but just before you post, you should select the item on the line again, so it will populate the other fields on the journal line.
Also, I noticed that the VAT posting group is empty, that could also cause issues later on, but lets worry about the GPPG first.
