ESP8266 RF2: only GPIO 5 allowed on Wemos D1 Mini Pro V3.0.0?

I think I miss something. If I download the source code, make my changes as described Flamingo sf-501 remote and upload it to my device (Visual Studio Code + platformio), than I don’t get a SSID from the device.

Do I have to enable the wifi manager manually somewhere?

grtz
B