If you have previously purchased a GigSky data plan and still have the eSIM installed on the phone, you do not need to be connected to Wi-Fi. The GigSky service will allow you to connect and purchase a data plan.
If you have not previously purchased a data plan or deleted the eSIM from your phone, you will have to be connected via Wi-Fi to purchase a data plan.
If you have any further questions, please contact GigSky Support at support@gigsky.com