I have a Heights WiFi 6 HT-178AX router (Rebel Internet) and I'm trying to add the RE705X to the router as part of the EasyMesh system. 
 

When I first plugged it in I used the Tether App and it added it as a range extender. With the router name.ext.

the Tether app only allows you to select OneMesh and not EasyMesh.

I tried to access the tplinkrepeater and tplinkwifi but kept getting an error message. Tried connecting directly to the RE705X by both the  TP WiFi name and by .ext name and get the same error.
 

I carried out a hard reset on the RE705X. Then used the WPS on the router and RE705X to connect. It created a router.ext WiFi. If I try to connect to it it says the password is incorrect. Try to put in the router password and it says it's incorrect.

Tether App is saying 'no devices found'.

Network is showing Router.ext WiFi.

As it has created a .ext WiFi then I'm guessing EasyMesh is not working.

Can anyone advise what I've done wrong and steps to resolve please . Ideally to have the RE705X as part of the routers EasyMesh system?