Displaying Transaction Id to the customers view

I've been making an eCommerce laravel system and I've been struggling with showing the customers their transactions Id after they've completed all their payment. I'm using an API to carry out the transaction. After the user has successfully carried out the payment, the transaction Id is then saved to the database. Now, I want to take the transaction id, and display it on the customers view so that they can print an invoice. Here's the controller that's supposed to be handling all the transaction Id:

public function confirmPayment(Request $request){
    $request->validate(['transactionId'=>'required']);
    $transId = $request->transactionId;
    $exists = Payment::where('mpesa_trans_id',$transId)->latest()->first();
    if(!$exists){
        $error= ["success"=>false, "error"=>"Unable to confirm your transaction code. Please contact admin.. :)"];
        session($error);
        return back();
    }
    $message = ["success"=>true, "message"=>"Payment successful!"];
    session($message);
    return back();
}

Here's how I've tried to display the transaction id on the customers view

                        <div class="frm-grp">
                            <label>@lang('Transaction Id')</label>
                            <input type="text" name="transactionId" placeholder="@lang('Example: OIB9FQP9H7')">
                            <span class="text-box">Your Transaction Id Is</span>
                            <span></span>
                        </div>

Which also gives me an error 'Undefined variable: transId'. I didn't put the @foreach yet.

Can someone please assist me on figuring out the solution to this problem? This is where the transaction id is supposed to be displayed after the customer makes a payment

via Chebli Mohamed