Adding Pre-ynab debt to a card that had no prey nab debt but it won't let me establish the category.

When I opened my Amazon store card, there was no pre-ynab debt since I opened it after using ynab for a while. I recently made a large purchase that takes advantage of special 0% financing for 6mos and would like to establish this a "pre-ynab debt" so that I can allocate money to pay it off over the 6 months. But when I try to add the category it says that the name has been reserved or that there is already a category with that name. I have expanded all my options under "pre-ynab debt" and it's nowhere to be found. Help!

EDIT: I see the category as the first transaction on my prime card. It reads " Pre-ynab debt: Amazon Prime Store Card" however, when I try to assign the transaction to that category, it does not pop up as an option.