can't save data, when create new data by same category

Model

error : "Array to string conversion (SQL: update spent_times set updated_at = 2018-10-23 09:16:43, spent_time = 16, percentage = 70, task_category = testing where id = 1) ◀"

public static function findOrCreate($plan_id, $data)
{
    $fromDate = Carbon::now()->subDay()->startOfWeek();
    $nowDate = Carbon::now()->today();

    $spent_time = static::where('plan_id', $plan_id)->first();

    if (is_null($spent_time)) {
        return static::create($data);
    }else{
        $new_spent_time = SpentTime::first();
        $task_category = $new_spent_time->task_category;
        $new_spent_time->spent_time = $new_spent_time::where('task_category',$task_category)
                                    ->sum('daily_spent_time', $new_spent_time->daily_spent_time , $fromDate);
        $new_spent_time['spent_time'] = $new_spent_time->spent_time + $spent_time->daily_spent_time;

        $new_spent_time->percentage = $new_spent_time::where('task_category',$task_category)
                                    ->sum('daily_percentage', $new_spent_time->daily_percentage, $fromDate);
        $new_spent_time['percentage'] = $new_spent_time->percentage  + $spent_time->daily_percentage;
        $new_spent_time->save();
        return $spent_time->update($data);
    }
}

and why is it only the first ID?

via Chebli Mohamed