FortiGate 100EF + TP Link Archer C20

Hello, I need your help. I have a network composed of 4 access points with a captive portal. - FortiGate 100EF captive portal - TP Link archer C20 Wifi terminals (X4) I can set the terminal in 3 modes (Wireless router, Access Point and Range Extender). I tried all 3 modes but it doesn't work. - I tried in Access Point mode using the captive portal but the 4 terminals together do not work (with one terminal it works). - I tried Range Extender mode but the portal doesn't work. - I tried with fixed IP address or DHCP but no difference. Could you help me with the configuration? Best regards, Nikolas