Laravel menampilkan beberapa nilai yang dipilih
$selected = explode(",", $products->supplier_id);
<select name="supplier_id[]" multiple="multiple">
@foreach($suppliers as $supplier)
<option value="{{ $supplier->id }}" {{ (in_array($supplier->id, $selected)) ? 'selected' : '' }}>{{ $supplier->name}}</option>
@endforeach
</select>
smtir