Hi keith-summers.
Being able to import information into your QuickBooks Online account is a great way to enter a lot of information quickly. I'd be happy to help you with getting your mileage imported into QuickBooks Online.
Currently the only file type that you can import into your QuickBooks Online Mileage tracker would be .CSV. As this is the only file type a json file will not be able to be imported without the use of a third party app or converting the file to .CSV. If you wish to use a third party app to import your information into your account you can click on the Apps link in the left hand menu of your QuickBooks Online account.
If you decide to get it converted into a .CSV file you can import it by going to Mileage>Arrow beside add trip>Select the appropriate import from option and follow the prompts.
If you have any questions let us know and we'd be happy to help.