I had a similar problem once when I was setting up a custom shop system in a game. For me, the fix was buried in the database settings. I had to adjust the stack limit for the item in the MySQL database, which allowed bulk purchases without triggering errors. You might want to check the item_template or a similar table for stackable values.
As for inspiration, I once played around with a different setup for fun using https://themulligans.org. While it’s an online casino, their sleek inventory and transaction systems gave me some cool ideas for designing in-game economies.
