Gemara cup lol
I wrote my post in haste and didn't bother checking the spelling. It's probably a bit difficult to understand what I wrote, but if you understood, thumbs up.
The same trick would work for Amazon using your GC, should you want to use an Amex offer that requires you to use at least one point. Let me play out the scenario for you.
An item you want to buy on Amazon costs $100. You have an Amazon GC worth $110. Now, you want to use your GC to cover the full balance, but you also want to use an Amex offer that gives you 40% off if you use one point.
So, buying an item for $50.02 would leave you with a GC balance of $59.98. The item will now cost $59.99 after applying the one point, allowing you to use the Amex offer and the GC. I haven't done this in some time, but back in the day, I had Dan write about it and DoC. It was a little trick to get both perks.
As for Instacart, I'm not saying it will work, but I'm just thinking out loud. Try the above for instacart and see of you can hold the balance and then cancel that order.
I got $50 off $100 from Walmart 6 time BH iber the summer, and I used each one with $15 back from Chase, buying items with a "buy 25 get 7" deal. This effectively lowered the amount I needed to spend while still getting $65 back. Just thinking outside the box will sometimes take you to new places you have yet to discover.