Javascript function does not send data into Laravel route

I have created this button:

<button onclick="addToFavourites({{ $product->prd_id }})" class="btn btn-primary">
     <i class="fa fa-heart"></i>
     <span>
        Add to favourites
     </span>
</button>

So as you can see I have added an onlick function named addToFavourites which goes here:

function addToFavourites(productId) {
            $.ajaxSetup({
              headers: {
                'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
              }
            });
            $.ajax({
                url: baseurl + "/add-to-favourites",
                type: "POST",
                data: {
                    prd_id: parseInt(productId)
                },
                dataType: "json",
                success: function (output) {
                    $('#afterAddToFavourites').modal('show');
                }
            });
        }

So this function will call the route with URI of add-to-favourites with POST method:

Route::post("add-to-favourites", "ShopCartsController@addToFavourites")->name('addToFavourites');

And in the CartsController:

public function addToFavourites()
{
    $favPros = new FavouriteProduct();
    $favPros->user_id = auth()->user()->user_id;
    $favPros->prd_id = request()->prd_id;
    $favPros->save();
}

But now the problem is whenever I click on the button, it does not do anything at all!

And at the Console, I see this error:

POST https://sitename.com//add-to-favourites 500 (Internal Server Error)
send @ jquery.js:2
ajax @ jquery.js:2
addToFavourites @ProductName:1187
onclick @ProductName:458

But I don’t what’s going wrong here and how can I fix this…

So if you know, please help me out cause I really need this…

Thanks in advance.