Payment Gateway API

hi, would like a payment gateway created and linked with my website. kindly read the documentations provided in the link [login to view URL] when a client purchases an e-book from my website, he/she would then submit a transaction reference number that he/she received from the payment gateway. The code that you would create should be able to check the whether the transaction reference number is on the payment gateway server or is invalid. If it confirms it is available on the Payment Gateway server the code should immediately initiate a download of the e-book and redirect the client to a thank you page with the website. In summary this is what your code should be able to achieve; 1) List the e-books being offered by the website have shopping cart. 2) the code should prompt the client to pay X amount on check out and provide a submission box for the client to be able to submit the reference number that he/she receives from the payment provider. 3)The code should check for the reference number and confirm if it is valid or not. 4) The code should the initiate a download of the e-book or e-books if reference code is valid or request the client to submit the correct reference number if invalid. In case of further explanations i will be ready to provide.