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4.2. Reading the response
Response The response will be in XML format. You must extract the value of the URL that you will need to redirect the customer to. You may validate the response by simply checking if it starts with "http". If it doesn't start with "http" then the response is an error message. The URL length will be up to 80 characters"<url_payment>" tag, which should contain a valid URL. The customer should then be redirected to this URL. To validate the response, check if it is well-formed XML. If the response is not valid XML, treat it as an error message.
4.3. Receiving the IPN with the authorization response
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