I see.
The save code doesn’t actually carry over from game to game, what it does is show you a string that you can input again in another game which sets the properties to the correct values.
First, you should test the decoding system during the same game you use the encoding system to see if it works normally.
Then, try setting the Save Code property to the output of the encoding system from a previous game, and seeing if it returns the money from that.
Then, if that works, you can make an in-game keyboard so you can type in previous save codes. The keyboard should update the Save Code property.
Unfortunately, making keyboard is a lot of work, and I really hate to ask you to do more after spending so much time on this mechanism to no avail. Here’s the guide for it (Made by the same person!):
You might also have to add symbols, capital letters, and numbers to the keyboard, since the save encoding system uses every character. 