Hello,
Just to confirm, are you using the latest version of the ‘INKBIRD’ app?
During the pairing process of ITC-306A, is its WIFI indicator always on/flashing/disappearing?
Just in case, please make sure the phone’s Bluetooth and location functions are turned on, and it is connected to 2.4GHz wifi; the router has no limit on the number of connected devices.
For more troubleshooting, please refer to: