@YazD148 Had the same issue and determined that the password was not correctly set when using the TP-Link Tether App. I recommend that you factory reset the extender and use the web management tool...

@Tony To clarify: Does the RE505X support 802.11 ax (WIFI 6) in AP Mode? I am running v1.08 firmware and the UI still does not include an option for WIFI 6.