Flashing the ER-X can be a bit challenging due to a 2 stage install, changing ports, and low level command line tasks. This is the checklist I use.
Phase 1: Flash Althea Firmware
- Download the erx-factory.tar file
- Download the erx sysupgrade file from Althea’s firmware page
- Set computer ethernet port to a manual IP like 192.168.1.11netmask255.255.255.0
- Connect cable to ER-X port eth0
- Browse to https://192.168.1.1
- Login with username ubntpasswordubnt
- Say no to config wizard
- Click system button in bottom left
- Upgrade System Image,
- Select the erx-factory.tarimage, confirm twice
    (router reboots into commandline-only OpenWRT image)
- Switch cable to eth1 port, wait for about 1 minute
- Ping 192.168.1.1 to confirm it’s working
    $ ping 192.168.1.1
- Transfer the sysupgrade image to the device using ‘scp’
    $ scp ./erx-sysupgrade.bin root@192.168.1.1:/tmp/erx.bin
- ssh into device
    $ ssh root@192.168.1.1
- Run sysupgrade with the uploaded image:
    $ sysupgrade -n /tmp/erx.bin
- Change computer ethernet port to DHCP
- Move cable to ER-X port eth4
- Ping 192.168.10.1 to confirm
Phase 2: Configure Althea Router
- Browse to http://192.168.10.1 (important: http:// NOT https://)
- Change Eth0 port from WAN to LAN or Mesh
 (WiFi and Ports → Ports)
- Set a Nickname
 Settings → Nickname
- Set Operator Payment Address
 (Advanced → Network Organizer → Organizer Payment Address)
- Enable Selling Bandwidth
 (Advanced → Selling Bandwidth)
- Check that the relay neighbor is visible
 (Selling Bandwidth → Neighbors)
- Disable Selling Bandwidth (optional)
 (Advanced → Selling Bandwidth)
- Add Exit Node (requires a working mobile SMS number to confirm)
 (Settings → Exit Node)
- (Optional) Transfer xDai funds using MetaMask to the router’s payment address
 (Advanced → Node Information → Payment Address)
- Complete remaining tasks on the Dashboard:
- Save Contact Info, Backup Wallet, Set WiFi SSID & Password, etc
Phase 3: Command Line
- Install packages
opkg update
opkg install nano
opkg install iperf3
- Add remote admin SSH keys to /etc/dropbear/authorized_keys