When you create a new button, the property "item_name" is never set. That's because in the Paypal.php component file, there's a line that says

      $item_name = Settings::get('item_name');

However, 'item_name' is not a setting, but a property. This means you should have:

      $item_name = $this->property('item_name');

I agree with this. fix the problem here. Replace in paypal/default

<input name="item_name" value="{{ __SELF__.property('item_name') }}" type="hidden">