Answers for "carbon::now() plus 1 day"

add seconds to datetime carbon

Try to parse() it first:
$date = Carbon::parse($dateTime)
            ->addSeconds($seconds)
            ->format('Y-m-d H:i:s');

laravel carbon created_at date in current month

public function myMonthApts()
{
        return $this->appointments()
                        ->whereIn('status_id', [3,4])
                        ->whereYear('created_at', Carbon::now()->year)
                        ->whereMonth('created_at', Carbon::now()->month)
                        ->count();
}