Hi Víctor,
To retrieve parameters a function must be initialized with PYFN_FLAGS::KEYWORDS. Then use pylib.ParseTupleAndKeywords() to get the value for each parameter.
The following code shows the implementation of a function which expects a string, an integer and a float:
static _PyObject *extendpyapi_PassParameters(_PyObject *self, _PyObject *args, _PyObject *keywords)
{
	PythonLibrary pylib;
	String str;
	Int32 integer = 0;
	Float real = 0.0f;
	const Char *kwlist[] = {"str", "integer", "real", nullptr};
	if (!pylib.ParseTupleAndKeywords(args, keywords, "$if", kwlist, &str, &integer, &real))
		return nullptr;
	if (str.Content())
		GePrint("Parameter str: " + str);
	GePrint("Parameter integer: " + String::IntToString(integer));
	GePrint("Parameter real: " + String::FloatToString(real));
	return pylib.ReturnPyNone();
}
...
moduleFunctions[1].Init("PassParameters", (PyFn)extendpyapi_PassParameters, PYFN_FLAGS::KEYWORDS, "PassParameters() - Extend Python API");