Wwan router with wlan

I'm a new Openwrt user.
I have installed Openwrt Community Firmware r13342 on a Linksys wrt1900acs device.
I have to make use of a wwan ISP.
I have configured Openwrt as a wifi client with help of https://openwrt.org/docs/guide-user/network/wifi/connect_client_wifi using the Luci GUI.
I have access from the lan with ethernet to internet, so that is oke.
For the wifi client I use radio0, this is the 5 ghz radio.
Now I want to use radio1, this is the 2.4 ghz radio for wireless lan clients, so Openwrt act as a wireless Router. When I add this second wifi network as a master the first (radio0) stops working.

Please help me to configure this router with a wifi client (wwan) interface and a wifi lan interface with the Luci GUI.