Error when opening notebook files

I followed the instructions, tried it on two different computers but each time I open a notebook file I receive the below error (any ideas as to how I can fix this?):

Fetch content failed
syntaxerror: unexpected token < in JSON at position 5

Figured out the issue was the notebook files on github. Downloading them from the actual lectures worked, but now I receive an error when trying to run cells:

“Launch kernel failed”
A Kernel named julia-1.0 does not appear to be available. Try installing the julia 1.0 kernelspec or selecting a different kernel.

Tried using “build IJulia” but that didn’t work.

Had to click runtime > then the julia version before clicking run cell. Disregard.