Generic Exponential Backoff Retry Mechanism C++11

I have written a generic exponential backoff retry loop in C++11. I'm using std::function to pass the callable to retry loop. callable will be retried if isRetriable function returns true.

#include <algorithm>
#include <cassert>
#include <chrono>
#include <functional>
#include <iostream>
#include <thread>

constexpr int64_t max_backoff_milliseconds = 30000; // 30 seconds
template <class R, class... Args>
R Retry(int max_retry_count, int64_t initial_dealy_milliseconds,
    const std::function<bool(R)> &isRetriable,
    const std::function<R(Args...)> &callable, Args &&... args) {
    int retry_count = 0;
    while (true) {
        auto status = callable(std::forward<Args>(args)...);
        if (!IsRetriable(status)) {
            return status;
        }

       if (retry_count >= max_retry_count) {
           // Return status and abort retry
           return status;
       }
       int64_t delay_milliseconds = 0;
       if (initial_dealy_milliseconds > 0) {
           delay_milliseconds =
               std::min(initial_dealy_milliseconds << retry_count,
                     max_backoff_milliseconds);
       }
       std::cout << "Callable execution failed. Retry Count:"
              << retry_count + 1 << std::endl;
       std::this_thread::sleep_for(
           std::chrono::milliseconds(delay_milliseconds));
      retry_count++;
   }
}

bool isRetriable(int status) {
    if (status == 5)
       return true;
    return false;
}

int foo(int x, int y) {
    static int a = 1;
    a += (x + y);
    return a / 6;
}

int main() {
    auto result = Retry(1000, 100, isRetriable, foo, 1, 3);
    std::cout << result << std::endl;
    return 0;
}

When I compile it, I'm getting below error:

prog.cpp: In function ‘int main()’:
prog.cpp:50:71: error: no matching function for call to ‘Retry(int, 
int, bool (&)(int), int (&)(int, int), int, int)’
auto result = Retry<int, int, int>(1000, 100, isRetriable, foo, 1, 3);
                                                                   ^
prog.cpp:11:3: note: candidate: template<class R, class ... Args> R 
Retry(int, int64_t, const std::function<bool(R)>&, const 
std::function<_Res(_ArgTypes ...)>&, Args&& ...)
R Retry(int max_retry_count,
^~~~~
prog.cpp:11:3: note:   template argument deduction/substitution failed:
prog.cpp:50:71: note:   mismatched types ‘const 
std::function<int(_ArgTypes ...)>’ and ‘int(int, int)’
auto result = Retry<int, int, int>(1000, 100, isRetriable, foo, 1, 3);
                                                                   ^  

Could someone explain to me why I have this error?