I only needed one more item to “unlock extra savings up to 15%”, so I added an extra item to see what the savings would be. I didn’t think the savings matched what was advertised, so I removed an item to see what the difference was (making sure to screenshot before/after this time). Turns out the price of 3 out of 4 items is the same after an extra 5% discount.
I followed up with customer support. They said go ahead with the order and they will refund me the amount after. They gave me a $5 credit for my trouble. They said they would escalate this issue to the development team.