This is not how you load data from json file into the array..
You need to change your code like this:
Note, that "For each element" loop is a sub-event under "On start of layout".
Also, you have a very inefficient way of storing level objects in the array. You are basically designing the level in the array with numbers. Why not draw it on the TileMap in layout editor? It will be much easier.
The traditional method is to store object types and their coordinates, something like this:
wall, 100, 50
wall, 120, 50
wall, 150, 50
chest, 200, 100
zombie, 300, 120
Of course, you don't enter these numbers manually, you prepare them using some kind of level editor.