Xcode header file not found

In my iOS project I have many libraries which require

#include "config.h"

However in the latest version of Xcode I am getting an error "config.h" file not found which means that Xcode cannot find the header file.

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The file is actually inside the root of the project folder.

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This is what I put inside "Header Search Path" in the build settings of the app target: enter image description here

But this still give the error above. Any hints on how to fix this?