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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