Error - Severity: Notice-->Undefined property: stdClass

I am getting the following error messages

Severity: Notice  --> Undefined property: stdClass::$service_name /home/examprep/public_html/application/controllers/payment.php 194
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$transaction_reference /home/examprep/public_html/application/controllers/payment.php 196
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$internal_transaction_id /home/examprep/public_html/application/controllers/payment.php 197
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$transaction_timestamp /home/examprep/public_html/application/controllers/payment.php 198
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$transaction_type /home/examprep/public_html/application/controllers/payment.php 199
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$amount /home/examprep/public_html/application/controllers/payment.php 200
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$first_name /home/examprep/public_html/application/controllers/payment.php 201
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$last_name /home/examprep/public_html/application/controllers/payment.php 202
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$middle_name /home/examprep/public_html/application/controllers/payment.php 203
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$sender_phone /home/examprep/public_html/application/controllers/payment.php 204
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$currency /home/examprep/public_html/application/controllers/payment.php 205
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$account_number /home/examprep/public_html/application/controllers/payment.php 206
ERROR - 2017-05-12 01:21:11 --> Severity: Notice  --> Undefined property: stdClass::$signature /home/examprep/public_html/application/controllers/payment.php 212


My payment controller is as follows

     $base_string =  "service_name=".$callBack->service_name.
                        "&business_number=".$callBack->business_number.
                        "&transaction_reference=".$callBack->transaction_reference.
                        "&internal_transaction_id=".$callBack->internal_transaction_id.
                        "&transaction_timestamp=".$callBack->transaction_timestamp.
                        "&transaction_type=".$callBack->transaction_type.
                        "&amount=".$callBack->amount.
                        "&first_name=".$callBack->first_name.
                        "&last_name=".$callBack->last_name.
                        "&middle_name=".$callBack->middle_name.
                        "&sender_phone=".$callBack->sender_phone.
                        "&currency=".$callBack->currency.
                        "&account_number=".$callBack->account_number;
        //$payment_info->mpesa_api_key;
        $symmetric_key =$payment_info->mpesa_api_key;
        $signature_created = base64_encode( hash_hmac("sha1",$base_string,$symmetric_key,true));

How do I resolve the error message?

What is the value of $callback? This seems to be your error.

Also note that your should ask these questions in the appropriate subforum, this definetly does not belong in "Choosing CodeIgniter"