Please look over below code

   public function paypalNotify(Request $request, $transaction_id){
        //todo: need to  be check
        $payment = Payment::whereLocalTransactionId($transaction_id)->where('status','!=','success')->first();

        $verified = paypal_ipn_verify();
        if ($verified){
            //Payment success, we are ready approve your payment
            $payment->status = 'success';
            $payment->charge_id_or_token = $request->txn_id;
            $payment->description = $request->item_name;
            $payment->payer_email = $request->payer_email;
            $payment->payment_created = strtotime($request->payment_date);
            $payment->status = 'declined';
            $payment->description = trans('app.payment_declined_msg');
        // Reply with an empty 200 response to indicate to paypal the IPN was received correctly
        header("HTTP/1.1 200 OK");

Your payment are succeeding here $payment->status = 'success';

Please read carefully your payment gateway instructions to achieve IPN request or something like that

Best regards