"You are not connected to the Miku. Please go back to retry. If the problem persists, please tap here for help." 

You are trying to connect your Wifi setting to the Miku. It's name in the wifi list of your phone's settings should be of the form, "Miku-<number>".

• Sometimes your phone takes a few seconds to connect to the Miku. Please wait for the Wifi indicator to on your phone to show it's connected to Wifi and not your mobile data connection.
• Sometimes the phone may drop the connection to the Miku. If this occurs you need to hit the back button in the app, reconnect to the 'Miku-<number>' Wifi in your phone's settings and retry.
• Turn off Wifi Assist: Go to Settings > Cellular or Settings > Mobile Data. Then scroll all the way down and near the bottom tap the slider for Wi-Fi Assist to turn it off (https://support.apple.com/en-us/HT205296). Then go back and reconnect to the 'Miku-<number>' Wifi in your phone's settings and retry. Don't forget to reverse this setting after pairing with your Miku.
• If turning off Wifi Assist doesn't work, turn off Cellular Data: Go to Settings > Cellular or Settings > Mobile Data. Then tap the slider for Cellular Data to turn it off. Then go back and reconnect to the 'Miku-<number>' Wifi in your phone's settings and retry. Don't forget to reverse this setting after pairing with your Miku.