C++ template function with std::optional

Question

Attempting to use a template class inside of an optional i.e. std::optional<T> as a function parameter for a templated function that does the following. If the std::optional<T> param is truthy, then uses the << operartor to write param.value() to a std::ostringstream.

#include <iostream>
#include <sstream>
#include <optional>
#include <string>

template<typename T>
std::string send(int number, std::optional<T> param)
{
    std::ostringstream oss;
    oss << std::to_string(number);

    if (param)
    {
        oss << " " << param.value();
    }

    return oss.str();
}

// Works just fine
// template<typename T>
// std::string send(int number, T param)
// {
    // std::ostringstream oss;
    // oss << std::to_string(number);

    // if (param)
    // {
        // oss << " " << param;
    // }

    // return oss.str();
// }


int main()
{
    std::cout << send(1, {3});
    return 0;
}

However, the code above throws

error: no matching function for call to 'send'

note: candidate template ignored: couldn't infer template argument 'T' std::string send(int number, std::optional param)

Compiler command

clang++ main.cc --std=c++17

I don't quite understand why the compiler cannot infer the template argument here. Even when I specifically instantiate the template for a specific type as such.

template std::string send(int number, std::optional<int> param);