Struct in two differents files

I have a basic main.cpp file and another file with a header (I will call it test.cpp and test.h).

From the main.cpp I would like to call a function in the test.cpp which returns a struct and it does not work. Here is what I have tried:

Main.cpp

#include <Test.h>
using namespace std;

struct Output
{
  cv::Mat Tcw;
  int state;
};

int main(int argc, char **argv)
{
  struct Output tempOutput = foo(frame, timeStamps);    
}

Test.h

#ifndef TEST_H
#define TEST_H

struct Output
{
  cv::Mat Tcw;
  int state;
};

struct Output foo();

#endif

Test.cpp

#include "Test.h"  

struct Output foo()
{
     cv::Mat mat;
     int i = 3;
     return {mat, i};
}

I have this error: error: conversion from ‘foo’ to non-scalar type ‘Output’ requested