Delete multiple record return 500 Server Error

Hi, I want to delete multiple record using checkbox, but it always return 500 (Internal Server Error). Here's the controller:

public function removeSelected(Request $request)
    {
        foreach($request['id'] as $id){
            $user = tap(User::findOrFail($id));
            $user->delete();
        }
    }

and here's the route:

Route::post('users/remove', 'UserController@removeSelected')->name('users.remove');

At the blade template, I use this button code (button outside form)

<button onclick="deleteAll()" class="btn btn-danger btn-sm"><i class="fa fa-times"></i> Remove Selected</button>
{{ Form::open(['method' => 'POST', 'id' => 'form-users']) }}
    table content
{{ Form::close() }}

Everything works fine with no error result at blade view, error appear when I click at the button. The error message aside from 500 (Internal Server Error) is Invalid argument supplied for foreach().

Thank you.

Edit, here's the jquery code:

function deleteAll(){
    if($('input:checked').length < 1){
                swal({
                    title: 'Notice',
                    text: 'Please select user(s) to remove',
                    type: 'warning',
                    html: true,
                    confirmButtonColor: "#DD4B39",
                    confirmButtonText: "Confirm",
                });
            }else if
            (
                swal({
                    title: 'Warning',
                    text: 'Are you sure to remove the selected user(s)?',
                    type: 'warning',
                    html: true,
                    confirmButtonColor: "#DD4B39",
                    confirmButtonText: "Yes",
                    showCancelButton: true,
                },
                function(isConfirm) {
                    if (isConfirm) {
                        $.ajax({
                            url : "{{ route('users.remove') }}",
                            type : "POST",
                            data : $('#form-users').serialize(),
                            success : function(data){
                                swal({
                                    title: 'Removed',
                                    text: 'All selected post(s) have been removed.',
                                    type: 'success',
                                    html: true,
                                    confirmButtonColor: "#DD4B39",
                                    confirmButtonText: "Confirm"
                                }),
                                Pace.restart(),
                                $('table.display#tb_users').DataTable().ajax.reload();
                            },
                            error : function(){
                                swal({
                                    title: 'Error',
                                    text: 'Something went wrong.<br/>Can\t remove selected user(s).',
                                    type: 'error',
                                    html: true,
                                    confirmButtonColor: "#DD4B39",
                                    confirmButtonText: "Confirm",
                                });
                            }
                        })
                    }
                })
            );
        }