The desired Integration site on ModX with the payment system Robokassa

Need to integrate online store software site on CMS of ModX Revolution 2.7.1 with the payment system Robokassa. On the website of the payment system has all the code examples docs.robokassa.ru/#1275 the Website sells "keys" software. The customer should be generated and sent to the e-mail key. Key generation happens on reservere of the customer (the developer would "pull" through the request url, to get the answer key and send). Cm. enclosure. – detailed description. The deadline is 14 calendar days.