I have an Archer AX21 router that works fine as a router for my network.  My internet service is provided by Verizon.  Within the last week I bought 3 Deco AX 3000 WiFi 6 mesh units (Deco X55) to improve WiFi.

I don't use the WiFi servise on the AX21.  I turned both bands (2.4 and 5.0) off and use the AX21 for all router functions other than Wifi.  I set up the 3 Deco units using ethernet backhaul for all of them.  I use the three Deco units as Access Points only and they provide the WIFi signal (bands 2.4 and 5.0) and route incoming traffic to the AX21.  Everything seems to work fine with wifi traffic as well as some ethernet traffic.   I have an Amazon Alexa Echo Dot.  An old one and a fairly new one (2 years old).  The old Alexa dot works fine and I use it often.  The newer Alexa Dot will not connect to the internet.  I have gone through connecting it using the instructions in the Alexa app.  I used the Alexa app on my Galaxy phone and also the Alexa App on my Ipad.  When I get the Alexa Dot set up and ask it to do anything other than tell me the time, it responds that it is not connected to the internet. I turned on the 5.0 radio band in the AX21 router and the Alexa dot worked properly. When I turn off the AX21 5.0 band, the Alexa dot cannot connect to the internet.  I prefer not to have the AX21 radio band on.  I want to separate the wifi duties from other router duties.

Any suggestions.