Laravel邮政路线与参数

Im trying to do a post request via a form in my blade template with a parameter in the url . Here is my form:

<form action="/products/{{$produit->id}}" method="post">
     {{ csrf_field() }}
    <input type="text" name="avis_body" />
    <input type="submit" value="Send" />
</form>

Here is my web.php:

Route::post('/products/{$id}', function($id){
    return $id;
});

I don't know what im doing wrong. Im receiving this error:

Remove the $ from route declaration:

Route::post('/products/{id}', function($id){
    return $id;
});