typedef unsigned char GByte;

void someFunFromC(GByte* data);

someFunctionFromC(data: kotlinx.cinterop.CValuesRef<libmylib.GByteVar /* = kotlinx.cinterop.UByteVarOf<libmylib.GByte /* = kotlin.UByte */> */>?)

val kotlinString = "this is a Kotlin String"
someFunctionFromC(kotlinString.cstr)

Required : CValuesRef<GByteVar /* = UByteVarOf<GByte /* = UByte */> */>?
Found : CValues<ByteVar /* = ByteVarOf<Byte  /*>

kotlinString.toUtf8().toUByteArray().usePinned { kString ->
    someFunctionFromC(kString.adressOf(0))
}