@norvad Good day,
If House Leds are ON on both power line units , you could try some suggestions here:
1> change a different Ethernet cable between Main router and main power line adapter
2> try a different LAN port on main router.
If still the same problem,please connect a computer to router by Ethernet cable ( same cable that main powerline adapter is using) and check do you have any Internet?
How many Leds are ON on the main adapter and powerline extender?
If connected to the powerline extender by wire, what is the IP address & Gateway on your computer? https://www.tp-link.com/support/faq/838/