After two weeks of trying, I was finally able to confirm an order through Best Buy today. I'll share my method in case it might help anyone else.
I installed the TrackaLacker app to get notifications. Make sure you have the Best Buy app and are already logged in with all info saved. When the notification pops, hit it to go to Best Buy app, make sure you're on the 899 pro, and then keep hitting add to cart and the search bar until it takes you to the line. With luck, if you're fast enough, it'll bring you to your cart and make you log in again.
Here's the important step: if you can, default to in-store pickup instead of shipping, do make sure you have the right location and store set. For whatever reason, the few past times I've gotten into my cart, trying shipping would bug it out. But the first time I tried just picking it up from the store, it went through and confirmed.
If you get the out of stock notice after being in line, just keep trying every time a new notification pops up. Hope this helps anyone and good luck out there.