ONet Registration fix for iOS devices

From settings select Onet Wifi

That will redirect you to the ONet captive portal. Click on Continue

Select an authentication method on the next screen

After authenticating you should be connected to Onet, but you may receive the following error

If you are prompted to use Onet without internet select that option

If you are not automatically prompted to use Onet without internet click on Cancel then Use Without Internet

You should now be connected to Onet