PHP Callback Page from GT pay Gateway - open to bidding

I have a call back page or a gateway that sends the following information Transaction Requery: On transactions completion, it is imperative for the merchant to requery the status of the transaction to verify the transaction status at gateway. This is to eliminate man in the middle attack. Parameter( Case Sensitive) Description mertid This is the GTPay assaigned merchant id amount Transaction amount in kobo tranxid The Transaction ID hash sha512 hash of the following : mertid + tranxid + hashkey hashkey hashkey will be provided on setup. Please keep the value secure. Sample REST Request [login to view URL] Sample json Request [login to view URL] Sample json Response {"Amount":"200000","MerchantReference":"ZIB|WEB|IthenaL|6-03-2014|011592","MertID":"212","ResponseCode":"00","ResponseDescription":"Approved by Financial Institution","TransactionCurrency":"566"} ----------------------------------------------------------------- So given the following <?php $gtpay_tranx_id = $_POST['gtpay_tranx_id']//Transaction id $gtpay_tranx_status_code = $_POST['gtpay_tranx_status_code']//'==> 00 $gtpay_tranx_curr = $_POST['gtpay_tranx_curr']//'==> NGN $gtpay_tranx_status_msg = $_POST['gtpay_tranx_status_msg']//'==> Approved by Financial Institution $gtpay_tranx_amt = $_POST['gtpay_tranx_amt']//'==> 140000.00 $gtpay_cust_id = $_POST['gtpay_cust_id']//'==> destiny@[login to view URL] $gtpay_echo_data = $_POST['gtpay_echo_data']//'==> Transaction ID:AS20170222150106;ClientName: Destiny Amana [Icecool Contracts Limited]: Purchase of Basic Plus $site_redirect_url = $_POST['site_redirect_url']//'==> [login to view URL] $gtpay_gway_name = $_POST['gtpay_gway_name']//'==> webpay $gtpay_tranx_hash = $_POST['gtpay_tranx_hash']//'==> CDFB59FDBCE4DCCC7A1348EFF165AC2AA1438356FE042D0DCD5F39DD4DF3F7F4C79BDCF586B858626748CCD0D79B6A39D9A1532949FA5FB7C4E4CBAD3774D335 $gtpay_verification_hash = $_POST['gtpay_verification_hash']//'==> 7CBC424420E73377B6BB1B93979CED3D2A7C53576B13EC61B8F271CCF0025B1EFB4553592382559667560D8FCD3405FA2DC53AF18B6938AE55A67F37AB11F1F1 $gtpay_full_verification_hash = $_POST['gtpay_full_verification_hash']//'==> ED51E1CF82C3529D762F21453D5AC74A32F4D043A19CDBA3E3BF183CB3AC0866E58E3A99562E5AD23444040CD3D015643DFBA797CC4E3E4CF5496E554EECA2B0 $gtpay_tranx_amt_small_denom = $_POST['gtpay_tranx_amt_small_denom']//'==> 14000000 $hashkey = "D3D1D05AFE42AD50818167EAC73C109168A0F108F32645C8B59E897FA930DA44F9230910DAC9E20641823799A107A02068F7BC0F4CC41D2952E249552255710F" $merch_id = "3212" $valuetosend = $merch_id . $gtpay_tranx_id . $hashkey //The Sha512 happens here $hashvalue = hash('sha512',$_POST['valuetosend'] ,false) ?> Get the results in put into an array of variables which I can use in a form to pist to another page.