@Mr.X 

Hi, for your issue, please take the below anwser.

Our powerline device should work as this:  Only one main adapter should be connected to the main router by cable, then this one is used as sender unit.

The other powerline devices such as TL-WPA4220 will be used as receiver unit which receives internet from the sender unit via power line.

You just need to pair the sender and receiver unit together. For the connection and instruction to pair the two units, please follow the link. 

https://www.tp-link.com/support/faq/1089/

All of your wireless clients can connect TL-WPA4220's Wi-Fi to get internet.

Hope I have explained it more clearly for your issue.

If not, please let me know and I would like to explain it more clearly.

Good day!