Again, this is another example of the two application not agreeing. "Ei începeau școala la șase ani." is a valid answer on the phone app. Why not with online app?
"începeau școala la șase ani" was accepted
"used to" = "obisnuiau"
careful now, that's some advanced stuff there :)
Instead of "Ei", I used "EIe" and it was accepted per Duo.