@saltis99 I just thought about something else you could try first. Maybe WiFi connection specifically to Main Deco will be enough. Power off all Satellite Deco, so that only Main Deco is running, and...

@saltis99 This tool has about 80% success rate. Unfortunately, it is the only way to update Deco M9 Plus with firmware 1.2. Some people had success with Update Tool when they wired PC with Ethernet...

@saltis99 Shouldn't utility say "Deco M9 Update Assistant?" Did you follow correct link to download utility for M9 Plus (second link, not first that is for M5)?

@saltis99 You do not follow document correctly. Scroll down to Method 3: Method 3: Update the firmware via upgrade tool, which only applies to Deco M5 and Deco M9 Plus V2. open its text and follow....

saltis99 wrote @Alexandre. It says 1.2.11 Build 20190926 Rel. 55727 and also Your Deco Home Wi-Fi system is updated @saltis99 This is very old firmware (from 2019). Deco app can't update it, and...

@Baggers82 You can use two TP-Link powerline adapters, such as TL-PA7017 KIT. They should work together with Deco E4. Powerline link is very dependent on quality of electrical wiring and what is...