Configure Serial Port for Raspberry Pi

The Raspberry Pi (RPI) has the serial port (pins 8-Tx & 10-Rx) configured for a login shell by default, therefore you have to configure it for serial use in order for the Wireless Gateway to communicate with the RPI. 

Open up a terminal window and type:

raspi-config

Select "Interface options"

Then select "P6 Serial" option.

Say "No" to the question "Would you like a login shell to be accessible over serial"?

The reply "Yes" to the question "Would you like the serial port hardware enabled?"

Exit Save and Reboot. 

Special instructions for Raspberry Pi 3 and 4:

You need to disable Bluetooth so that the serial port will work.
Edit config.txt

sudo nano /boot/config.txt

Page down to the bottom of the file and add the following line:
Add the following line:

 

dtoverlay=pi3-disable-bt

Exit, save and reboot.