@DaveLen 

Hi, please confirm the below details then we will try to figure it out:

1. Are all the LEDs on the PA411 KIT correctly on, especially the powerline LED? 

2. If there is no internet, please press and hold the pair button for more than 6 seconds to reset the powerline adapter to factory defaults. Then repair them with the below instruction and give it a go.
https://www.tp-link.com/us/faq-258.html

After that, please connect your computer to the extender and check the IP address, default gateway, and DNS.
Note: How to get it: https://www.tp-link.com/us/faq-838.html (Please show us a screenshot of the status - details page)

Besides, please make sure that you can access the internet from the main router by a wired cable.

May it help.