Saving Object Values When Saving Game

I have written a class called “Inventory Slots.” These slots contain a type of blueprint that can be stored (base item) and the index in which it is stored. These slots are then stored in an array called “Item List” inside an inventory class. I want to be able to save the contents of this inventory in my Backpack variable. I have included my save code and the code that I use to call upon it. It seems to save when I call on my print statements, but then runs into errors as soon as I try to read what I have saved. Any help? Thank you so much in advance!