Firmware upgrade failing on Ubiquiti EdgeRouter X

Are you able to ping 192.168.1.20 from the pi when the router is in tftp recovery mode?

The article says if the network you're connecting the edgerouter to has a DHCP server then it will get it's IP from DHCP.

Also try using the discovery tool whilst in tftp mode to see if you can see the device.

You're not setting a netmask in the Pi. Enter 192.168.1.14/24 in the dialog. If you don't specify network size you don't get a route to other 192.168.1.0 via the Pi ethernet port.

if you haven't manually updated the bootloader tftp recovery won't be available, you will need to use the serial port