Why is Laravel Eloquent not updating the sum property on the model?

Question

Laravel

I get the model:
$order = Order::find(1);

In this model, you need to update status and sum
$order->status = "check";
$order->sum = 100;
$order->save();

As a result, the status is updated, but the amount is not, why? And if you give the model to the page, sum also comes without changes.

PS: it's probably the name sum, but changing it will be quite expensive