This is an iOS-generated error message specific to iPhone.
There are three common causes of this error.
The grill is already connected to a WiFi network
When pairing a grill manually (without a QR Code) the grill network name and/or password were entered incorrectly.
The phone is connected to a VPN, meaning the grill and the phone are connected to different networks and are unable to find one another.
Check to see if your grill is already connected to a WiFi network by navigating on the grill to Menu > WiFi Settings. If the SSID and Signal Strength fields are populated, the grill is already connected to a network. To resolve this, select Forget Network on the grill. Restart the grill and begin the pairing process again.
Restart the pairing process verifying the grill's network name and password are entered correctly.
Disconnect from the VPN and make sure that both your phone and your grill are connected to the same network.