Extend a hAP ac lite router with a TP-Link WR-841N V14.1, no internet

Hi!

First of all, I’m a very beginner with mikrotik and with networking.

I have a mikrotik router, configured with quick setup as Home AP Dual, on this side everything is working properly, if i connet to its wifi network (2,4Ghz).
But if i try to extend this wifi network with the above mentioned router/extender, I get no internet.
The TP-Link has a different SSID as the extended network.
If i connet to the extended network, i get no internet access, but i can still access the Mikrotik router through it without a problem.
The tplink works with a different (branded) root ap without a problem.

Am i doing something wrong?
Okay, its obvious that the problem is me, but please help.

At the moment there is no way to use different hardware than these.

Thank you!