Can't connect Amazon Echo Dot (Gen 3) with my Orbi RBR50

[AussieOrbi]

Hi, 

I've spent hours trying to work this out and slowly going insane. 

• I've got a Netgear Nighthawk X4S D7800 connected to an Orbi RBR50 with 2 x RBS50 satellites  
  • Orbi RBR50 and RBS50 on firmware V2.5.1.8 on a 5Ghhz connection
• I am trying to connect an Amazon Echo Dot (Gen 3) 

I plugged the Echo Dot in and downloaded the Amazon Alexa app. When I try to connect to the Orbi RBR50 network, it never works. If I connect to the nighthawk X4S network, it works everytime. Problem is all my smart home stuff is on the Orbi network and Alexa won't recognise the other devices because it's on a different network. 

I've tried the following steps than went through setup after each of these steps on the Amazon Echo Dot:

I've tried on the Echo Dot:

• Hard reset of Echo Dot by holding the setup button until factory reset
• De-registering the Echo Dot on Alexa app and re-registering
• Unplugged power and replugged power
• Set it up on Nighthawk network than change to Orbi network
• Reset all save passwords on my Amazon account and tried to reconnect to wifi network
• Uninstall Alexa app and reinstall Alexa app and setup everything 

I've tried on the Orbi network:

• Changing security method and trying to connect the Echo Dot
  • None - Doesn't work
  • WPA2-PSK - Doesn't work
  • WPA-PSK/WPA2-PSK - Doesn't work
• Change wifi password and reconnect Echo to new password
• Turned Nighthawk and Orbi off by the power source and turn back on
• Reboot Orbi network from the Orbi app
• Turned off Netgear Armor
• Turned off Netgear Armor and changed to none security method
• Created Orbi guest network with password security
• Created Orbi guest network without password security
• Un-install Orbi app and reinstall app and re-setup network from the beginning

I've read through every single previous post from other people that have problems connecting the Echo Dot to their Orbi network and none of the advice given there has worked. I don't know what else to do. It's driving me insane.

The Echo Dot connects to Nighthawk network with no problems so I know it's not the Echo Dot that's at fault. All my other devices connect to the Orbi network (Phone, computer, Sonos, etc) so I know the Orbi network works.

It just doesn't want to connect the Amazon Echo Dot and there is no way to see on the Orbi app if there is anything blocked while I don't have advance settings on the Amazon Alexa app to enter the network address etc. 

Please if anyone can help. Thank you

[FURRYe38]

What Firmware is currently loaded?

Did you disable the 5Ghz SSID Broadcast Under Advanced Tab/Advanced Settings/Wireless Settings. Then Try to connect the Dot? 

"I've tried on the Orbi network:

• Changing security method and trying to connect the Echo Dot
  • None - Doesn't work" < IF this fails then the Dot is faulty. Try another Dot. 

• What mode do you have your D7800 in? Modem only or router mode? 

This is a modem with built in router. Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop