... hmm, just installed b4r 3.71, but folder still contains older versions... - and is only named "b4r", not "b4r 3.71"
... or is rESP8266WiFi V 1.56 actual? Should not show the error: "rESP8266WiFi.cpp:99:14: error: 'class WiFiClientSecure' has no member named 'setInsecure'"...
I have a habit of adding the version number when installing a new version (I do the same for B4J & B4A), instead of using the default installation folder.
rESP8266WiFi is a wrapper for the actual Arduino library.
..thank you for hint, but in same source I need to use DFPlayer_Mini. By any reason, latest version B4R doesn't find the library. So I need to go back to B4R 2.51
but maybe reasen is arduino IDE too - I try it further :-(