I'd assume it's the balance remaining of the annual amount, since it's an "annual-billed-monthly" you bought a year so you pay for a year. I see no hints that it would be anything else.
I have to admit I don't understand why this is an upopular view. Do people think they should be able to buy a year subscription at a discount to the monthly rate, back out halfway through, and then be able to alter the terms of the deal they made?
Adobe can either (A) charge the full year up front, or (B) specify the full year cost and give customers the option to pay that monthly (like the buy now, pay later plans).
The issue is that their current wording is deceptive.
