Are you having a problem logging into WiFi via your Deco -- from a Windows computer?
I moved our Deco M9 + disks to our new home and connected them to a new Verizon FIOS modem and WiFi router. (4 July, 2020) The Deco lights are green and I could login to the internet from my iPhone. Everything looked good -- until I tried to login to the internet from my laptop (Windows 10 Pro). My laptop could 'see' the Deco M9 with strong signal strength. The Deco M9 will NOT transmit the correct WiFi password to the Verizon router, however; Windows always returns "invalid password"; see the screencap below. I can login to the Verizon router directly, no problem. I can also login via the Deco M9 with my iPhone, so the problem is unique to the Windows 10 laptop via the Deco M9,
The 'main' Deco is connected via an ethernet cable to the Verizon router. I reset both Decos, then installed the latest firmware via the Deco app on my iPhone.
My guess: There is a problem with the latest version of Deco firmware -- a conflict with login credentials passed by Windows 10.
If you are running to a similar problem, please post a reply below. I contacted TP-Link support and they replied the next day. I will let everyone know if they find an answer.