1. Connect your iPhone to the Wi-Fi network for your OBD2 adapter.
2. Open the Settings app, select Wi-Fi then select the blue info icon to the right of your OBD2 Wi-Fi network.
   
3. Make a note of both the IP Address and the Subnet Mask addresses.
4. Set Configure IPv4 to Manual and enter only the IP Address and Subnet Mask addresses from Step 3.  Leave Router blank.

private static final String TAXIMETER_CHARGE_BROADCAST = 
                                                "com.planetcoops.intent.action.TAXIMETER_CHARGE";

private final BroadcastReceiver mReceiver = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        // currency, see ITaximeterService.getCurrency()
        String currency = intent.getStringExtra("currency"); //NON-NLS

        /*
         * !! USE THIS TECHNIQUE TO CAPTURE THE FINAL VALUES CHARGED AT THE END OF THE HIRE !!
         *
         * The TAXIMETER_CHARGE Intent is broadcast when a charge is made (on transition
         * from STOPPED to FOR HIRE modes) and will carry the final values for the hire.
         */
        if (TAXIMETER_CHARGE_BROADCAST.equals(intent.getAction())) {
            // TAXIMETER_CHARGE intent
            Log.i(TAG, String.format(
                    "Taximeter Charge:\nExtras: %s%.2f\nFare: %s%.2f\nTax: %s%.2f\n" + 
                    "Total: %s%.2f\nDiscount: %s%.2f\nTip: %s%.2f\n",
                    currency,
                    intent.getDoubleExtra("chargeable_extras", 0d),
                    currency,
                    intent.getDoubleExtra("chargeable_fare", 0d),
                    currency,
                    intent.getDoubleExtra("tax", 0d),
                    currency,
                    intent.getDoubleExtra("total_fare", 0d),
                    currency,
                    intent.getDoubleExtra("discount", 0d),
                    currency,
                    intent.getDoubleExtra("tip", 0d)
            ));
        }

// Receive Taximeter updates
IntentFilter filter = new IntentFilter();
filter.addAction(TAXIMETER_CHARGE_BROADCAST); // Chargeable values
registerReceiver(mReceiver, filter);

We supply you with a volume license key (VLK) and the current version of the Taximeter APK file which you would then install on each device (see https://www.digitalcitizen.life/how-sideload-apps-using-apk-files-android-devices) .  The VLK is simply a case-sensitive string of characters which needs to be entered on each device.  The VLK will activate a predetermined number of devices which can be increased as and when required.  The activation is associated with each device and is not transferable.  Warning: Performing a factory reset or installing the app under a new user account (on devices which support multiple users) will cause its device identifier to be regenerated.  Reinstalling the app on a device which has been OTA upgraded to Android O or later may also generate a new device identifier.  As a consequence, a previously activated device will no longer be recognized by our licensing server and a new activation will be required.

Before entering the VLK, make sure you that you have an active internet connection, Wi-Fi or mobile data.  When you first run the app after installing the APK, the app will display the following alert complaining that the license check failed:

If you have already downloaded and installed Taximeter from the Google Play Store or install the APK using a licensed Google account and want to run it simultaneously on multiple devices, then the procedure is slightly different.  With an active internet connection, open the app on each device and navigate to Menu > Settings > Operator settings > Set volume license key (VLK).  Enter the key here then exit (Menu > Exit) and restart the app.

You can easily check whether a device has been successfully activated.  We append a "+" to the version information in the Menu > About screen to indicate that the app is volume licensed.