Set up Alexa in a Few Easy Steps. Learn how to set up your Echo device with our easy setup guide. Get tips on how to connect Alexa to the Wi-Fi, download the Alexa app, and more.
How to Connect to Your Home Router as an Administrator - Lifewire.

I have four HS103s all in the same room as my router and all connected to the same 2.4GHz access point. Problem is, one of the four will not work with Alexa. I can control it on my phone using the Kasa app and it shows in Alexa's list of dev.

Such details provide a deeper understanding and appreciation for Connect Alexa To Home Router.
Ensure your router is optimally positioned and that both your Sonos and Alexa devices are connected to the same network, ideally a stable 2.4GHz network for better range and penetration. Review your Router settings to confirm there are no unusual restrictions or conflicting IP addresses.

It acts as your main Wi-Fi router and also connects to your Zigbee bulbs and sensors. Next year, you add new Matter-enabled smart plugs. The Eero recognizes them automatically, no extra setup needed. You use Alexa to control everything, or the Eero app on your phone.
Also, please connect your computer to the router (either wired or wirelessly).