Resurrecting this thread due to encountering the same problem that has, seemingly, randomly started in the last two weeks. Currently using an iPhone XS.
I've used pop data 30 & 60 min sessions numerous times in the past and now all I see is an error message stating "Oops! Something went wrong on our end. You can try connecting again by starting a new session."
I've tried initializing over a dozen sessions across numerous days and times to no avail. I've uninstalled the app and rebooted my phone then reinstalled the app, reset my network connections, power-cycled my phone intermittently between the aforementioned steps, and still nothing.
Any insight from anyone, assuming you were successful in getting it up and running again?