Syncing a many-to-many with a pivot model with $touches does not touch related models · Issue #31597 · laravel/framework · GitHub
laravel - Cannot use belongsToMany to sync pivot data - Stack Overflow
Managing Pivot Data with Laravel Eloquent - Server Side Up
Laravel 5.5 Pivot Casting - Laravel News
GitHub - damianlewis/october-laravel-pivot: This package introduces new events for sync(), attach(), detach() or updateExistingPivot() methods on BelongsToMany relation.
Laravel Many-to-Many Relationship: How to implement It
Difference between attach() and sync() in Laravel | Sync, Content management system, Attachment