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Here is what I get with commas:

JSON2 - 2017-05-04_153109.jpg

Alright change that back. It looks like its being flagged because you're missing parentheses after JSON. Put one after JSON and then one after Headers"
You should just be able to copy and paste this into the cell
=VALUE(ImportJSON("https://min-api.cryptocompare.com/data/price?fsym=BTC&tsyms=USD","/USD","noHeaders"))

No, parentheses are OK. I suspect this version of Excel is pure garbage :(

Oh I didn't even notice it was excel. I'm using Google Sheets. Not sure about fixing it in excel, should work in Sheets just fine. Sorry about the confusion