Laravel eloquent where pivot null or less than

I have timestamp field, named closed, in pivot table for Many to Many relationship. I want to get items where closed is null or is less than a specific time. I tried the following:

// In model
public function jobEquipments($job, $one = false)
    {
        $nowDt = Carbon::createFromFormat('Y-m-d H:i:s', date('Y-m-d H:i:s'));
        if (!$one){
        return $this->belongsToMany(Equipment::class, 'cavity_actions', 'cavity_id', 'equipment_id')
                ->wherePivot('job_id', $job)
                ->withPivot('created_at','aid')
                ->wherePivot('closed',null)
                ->orWherePivot('closed','<',date('Y-m-d H:i:s'))
                ->orderBy('pivot_created_at', 'desc');
            }
.... 

I also tried to use $nowDt instead of date('Y-m-d H:i:s') in orWherePivot However, there is no change to the query result. i.e It looks like the same values without ->orWherePivot('closed','<',date('Y-m-d H:i:s')) clause. In my database, I'm pretty sure that there is enough records with closed datetime value less than Now.

via Chebli Mohamed