Before using Whatagraph's Data Transfer feature - you have to make sure to have an account set up on the Google BigQuery side. They have their own pricing which will depend on your particular needs. You can find more detailed information on their website. The most important part is that you have to set up your billing account, by adding your card (even if you will be using their free tier plan).
That being said if you are keen to try it out, you can always set up a free account that will not charge your card until you reach a specific data limit threshold.