Check the following points.
If the KATANA-AIR is visible as a device in the Bluetooth settings on the mobile device
If the mobile device's Bluetooth settings show that the KATANA-AIR is already paired, then unpair it.
For iOS
From the iOS "Settings" menu, select "Bluetooth," and if the KATANA-AIR is displayed as "Connected," tap "i" to unregister it. After that, turn Bluetooth off and back on again.
*At this time, leave "KATANA-AIR MIDI" unpaired and close the screen. If it was inadvertently paired, unregister it again.
For Android
From the Android "Settings" menu, select "Bluetooth," and if the KATANA-AIR is displayed as a paired device, tap the "gear" icon next to it. In the window that appears, unpair the device.
After that, turn Bluetooth off and back on again.
*At this time, leave "KATANA-AIR MIDI" unpaired and close the screen. If it was inadvertently paired, unregister it again.
If the KATANA-AIR is not visible as a device in the Bluetooth settings on the mobile device
On the mobile device, turn Bluetooth off and back on again, then start pairing on your KATANA-AIR to redo pairing. For details, see "Listening to Sound via Wireless Connection with a Mobile Device" in the KATANA-AIR Owner's Manual or KATANA-AIR EX Owner's Manual.