MakerWorld seems to be doing nothing regarding easily seeing which gift cards have been used, and which have not. I’ve got the solution! I just created this gift card tracker Notion template. Just click this link and install it, then add gift cards.
If you don’t have a Notion account, make one 
I highly recommend!
Hope this helps!
Just want to clarify that I get no benefit from the above link, I’m just sharing it to help you all out.
I use notes on the iPad.
I use the strike-out format for the text of those I have redeemed.
A simple way to achieve the goal.
I do not have whatever Notion is, it sounds posh.
Better tracking or integrating the gift cards into the shopping card check-out process has been requested by many. One shouldn’t have to use any external tool to do track them.
If integrating it into the check-out process takes too long, can @MakerWorld gray out gift cards that have a balance of zero in the interim?
You have to imagine they get an API ping callback each time one is used, they could update the card issued at that point.
This isn’t rocket science.
Yes, They can also show the balance of each card instead of having users to click a button to view. Some have raised concern that will increase API calls, but if all the cards starts with a constant value of $40 or whatever currency it’s on, and update it when the card is used, there shouldn’t be additional API calls.
Note if my guess is true.
They just update the value left when used. Most of the time it will be 0, but, sometimes a remaining balance will be there.
Either way, it stores a currency value in the DB table next to the gift card ID.
No subsequent API calls. This is DB design and API call 101 stuff.
I used to design massive systems.
I use obsidian to track myself, have used notion in the past, but obsidian is a more interesting tool to me - local and with standard markdown text files
So many posh people.
Notes FTW
I’ve never been called posh before, I’ll take it 
Notes is fine (now that it has been updated and you can at least reference other notes within it) but I use obsidian much more extensively and for many things - in a zettelkasten approach - that notes simply wouldn’t be able to handle, but whatever works for you
It’s like if a notes app and a spreadsheet combined, but then make it twice as cool.
I didn’t have a Notion, I was being Obsidian about it.
Baby-making apps, cool!