How to solve ADB device unauthorized in Android ADB host device?

Check and uncheck the USB Debugging option in the device. If that doesn't work unplug and plug in the USB a couple of times.

At some point, the device should show a message box to ask you to authorize the computer. Click yes and then the device will be authorized.

• Get the public key from the client phone (adb host)

  cat /data/.android/adbkey.pub

• copy the above public key to the target phone's /data/misc/adb/adb_keys location. (you may need to stop the adb daemon first with stop adbd)

  cat /data/misc/adb/adb_keys

verify both cat outputs match.

try restarting adb daemon on target start adbd or just reboot them.

If you are having problems reading or writing to ADB KEYS in above steps, try setting environment variable ADB_KEYS_PATH with a temporary path (eg: /data/local/tmp). Refer to that link it goes into more details

    "On the host, the user public/private key pair is automatically generated,
    if it does not exist, when the adb daemon starts and is stored in
    $HOME/.android/adb_key(.pub) or in $ANDROID_SDK_HOME on windows. If needed,
    the ADB_KEYS_PATH env variable may be set to a :-separated (; under
    Windows) list of private keys, e.g. company-wide or vendor keys.

    On the device, vendors public keys are installed at build time in
    /adb_keys. User-installed keys are stored in /data/misc/adb/adb_keys"