how to create relational select option ajax in laravel 8 - ajax

Question

I try to create a relational select option in laravel 8 using ajax but didn't work I get this error in the console: 405 Method Not Allowed
POST http://127.0.0.1:8000/decomptes/%7B%7B%20route(%20'getOperationsChantier'%20)%20%7D%7D 405 (Method Not Allowed)
the route
Route::post('/getOperationsChantier', [DecompteController::class, 'getOperationsChantier'])->name('getOperationsChantier');
the jquery code
$(document).ready(function(){
// When an option is changed, search the above for matching choices
$('#chantiers').change(function(){
$("#mySelect option").remove();
// $("#city option").remove();
var id = $(this).val();
$.ajax({
url : "{{ route( 'getOperationsChantier' ) }}",
data: {
"_token": "{{ csrf_token() }}",
"id": id
},
type: 'post',
dataType: 'json',
success: function( result )
{
$.each( result, function(k, v) {
$('#mySelect').append($('<option>', {value:k, text:v}));
});
},
error: function()
{
//handle errors
alert('error...');
}
});
}).change();
});
the function in the controller :
function getOperationsChantier( Request $request )
{
$this->validate( $request, [ 'id' => 'required|exists:chantiers,id' ] );
$chantierOperations = ChantierOperation::where('chantier_id', $request->get('id') )->get();
$output = [];
foreach( $chantierOperations as $chantierOperation )
{
$output[$chantierOperation->id] = $chantierOperation->operation_id;
}
return $output;
}
can someone help me this is the first time when I use ajax