@Jakis I think because the OneMesh function only works with the Wireless function, but as you also wanted the function to work in AP mode

  @Andrsouzaaa i use one RE450 in AP mode for create Wi-fi From my modem and one 450 for extended the wi-fi in my flat.

I have expected that with 2 RE450 i can make OneMesh network.

  @Jakis no, the mesh function only works with a router + repeater and both need to share this mesh technology, which in the case of TP-LINK is called OneMesh.