With the new eSIM on the Apple iPhone, the app has been modified for the iPhone to manage the eSIM for the phone only. Your iPad Apple SIM will work the same way it always did, you have to use the Settings -> Cellular Data to manage the Apple SIM. For other GigSky physical SIMs you may have, you need to go to app.gigsky.com to purchase data plans for those SIMs.
The web-based app (app.gigsky.com) will continue to work the same way it always has for physical SIMs and you can manage all GigSky physical SIMs from there.
If you have any further questions, please contact GigSky Support at firstname.lastname@example.org.