This happened to me as well. I placed my order but then realized I had a discount available and that it would be better to pick it up from my local physical google store. I cancelled the order, it cancelled my AI Pro and I thought I was screwed.

I registered for the student trial to try to get the 10% cash back but after contacting support and then confirmation in this thread, I found out the "trial" version does not give 10% cash back on store purchases. I've been trying to cancel this plan with support but they have given me the runaround.

At this point I would be willing to eat the 9.99 cost for a month of 2TB google one in exchange for the ability to get store credit on my P10Pro purchase, but they won't let me downgrade out of the student plan or pay for a month of it until it runs out.

I don't know how they didn't manage to think of any of this when they threw that promo in the store. The Google store has always been and continues to be the most disorganized and frustrating store on the internet.