sync() and attach() not working together?

In my controller first i attach array of ids like this for my additional fields:

$property->features()->attach($additional_ids);

Then im using sync() because i have checkboxes :

 $property->features()->sync($features);

But problem is when i have this then my attach() is not working. Any suggestion how can i fix this? When i remove this sync() my attach is working. So idea is that i have checkboxes for features, and i have input fields for some additional features.I store this ids in pivot table .

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