filter max date on intermediate pivot table

Hi i cannot do this.. I have a relationship many to many as defined

Invoice model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Invoice extends Model
{
    public $primaryKey = 'id';
    protected $fillable = [
        'user_id',
        'date_ins',
        'tas',
    ];

    public function user()
    {
        return $this->hasOne(User::class,'id','user_id');
    }

    /**
     * The roles that belong to the invoice.
     */
    public function shifts()
    {
        return $this->belongsToMany(Shift::class, 'invoice_shift')
        ->withPivot(['invoice_id','shift_id', 'shift_taken_id', 'shift_swapped_date','shift_taken_date', 'tas','msg','status_tas']);
    }

}

Then Shift model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Shift extends Model
{
    public $primaryKey = 'id';
    protected $fillable = [
        'code',
        'description',
    ];
    /**
     * The users that belong to the role.
     */
    public function invoices()
    {
        return $this->belongsToMany(Invoice::class, 'invoice_shift');
    }
}

in pivot table i have also a column called shift_swapped_date, I wanted just to retrieve the row that has max value of this date. I tried in the controller

        $invoices = Invoice::with('shifts')
        ->get();   
        $invoices->max('pivot.shift_swapped_date');

but doesn't work always gives to me all rows...with all dates Solutions? Thx