Error/problem with include

I have some source, sample from github in the scr directory

#include <filename.h>

and two files the include directory both fron from git hub where the source comes from
filename.cpp including filename.h

It compiles but include filename.h is underlined with a serpentine im main.cpp and in filename.cpp. and marked es error
First I just had the main.cpp and added the library via the library function, same problem.
What ist wrong, my PlatfornIO is latest version.

Platform Arduino with ESP8266
Need help, do not like errors even if it compiles, never know whats going wrong some day


If it compiles but has the IntelliSense does not recognize it, rebuild it. Ctrl+Shift+P → Rebuild IntelliSense.