Inventory system not working properly.

So I was taking a look out output logs and I noticed whenever I picked up an item it would say something like:

[2019.10.01-03.47.21:284][824]LogScript: Warning: Script Msg: Attempted to set an invalid index on array Inventory [-1/15]!

So I’m guessing it has something to do with my array set up.

If anyone wants to have a look at it here it is:
https://drive.google.com/file/d/15-4OML1NReNvPl4OtkGjhhOzdpsZ4lmE/view?usp=sharing

Google doc because it exceeded the upload limit here.