Hi @haunglu,
Welcome to the Roku Community,
Thank you for letting us know that you cannot cast the Hulu channel from your Roku TV to your iPhone. We apologize for the inconvenience this may have caused you, but don't worry, we are more than happy to help you with this issue.
If the other channels from your Roku TV are working when casting it with your iPhone it only means that your Roku TV is working fine with the casting. However, we recommend you try casting the Hulu channel from your Roku TV to a different device if it is available.
Please keep us posted.
Regards,
Riamie
Riamie D.
Roku Community Moderator