Hi Matt, I'm running into exactly the same problem H169 reported here.
I originally purchased the $14.99 assets tier. I then followed your advice in the comments to use Buy Now and pay the remaining ~$15 to unlock the Unreal project.
I've now paid $29.99 total ($14.99 + $15.00), but itch created two separate assets-tier purchases and the Unreal Project ZIP is still locked.
I've contacted itch support as well. If possible, could you provide/adjust a download key so the Unreal project is unlocked for my account? My itch account is AuraStudiosOfficial.
Thanks!