SXT Lite 5 have License only Level 3. For AP mode you need Level 4.
"Server/AP mode" is for PTP Bridge (Point-to-Point) with only 1 client.
If you want connect to PtMP (WISP Base Station), use "CPE mode". In "Wireless" you need choise "station" (CPE-router) or "station wds" (transparent) mode. Type SSID, Frequency, channel width and protocol (of Base station) in Wireless config. Password hidden in "Security Profiles".
Hello Dmitry, your text here gives me hope! I was having 2 SXT Lite 5 routers working fine with PTP Bridge mode (at server side) and Station bridge mode from the client side. My problem started when I wanted to add a 2nd client creating PtMP connection. You think this setup could be done using 3 SXT Lite 5 routers? I will try the settings you proposed above anyway! Thank you so much.