Currently there is no any Add-on which offer this functionality, so you have to create or import custom functions by Script Editor available in Tools menu (for Spreadsheet). Then re-paste the content of ImportJSON.gs from bradjasper's GitHub page and save it.
After that, you can use ImportJSON function, for example:
If you want to paste a JSON object you can use http://www.convertcsv.com/json-to-csv.htm to convert it to a CSV and then import that into Google Sheets.
If you want to rotate the data from columns to rows you can use http://www.convertcsv.com/transpose-csv.htm
I found this easier than messing with an addon script.
This might ...
I believe you can simplify the whole procedure by slightly tweaking your already existing formulas and using helper columns.
Please follow these steps:
You can use either open or closed ranges. BUT.
Make sure all of the ranges have the same amount of rows.
If not, it will just be messy :)
Create your helper columns somewhere on the same ...
The function ImportJSONBasicAuthentication is basically just a wrapper function for ImportJSONAdvanced but changes some options before calling it (the line with var fetchOptions initiliaztion call sets up options accordingly). You'd need to include the function ImportJSONAdvanced and any functions it might also call (dependancies).
Notice the return value ...
I believe that's relying on the the JSON import library by Chris Keller, found here.
As its description says,
To use go to Tools --> Script Editor and add the script and save.
This means the entire script, not just one function from it.