Odoo ERP Modification

Small private business supplying African Literature Lesson plans and aids for teachers. Using Odoo Web and ecommerce functionality with link to Payfast for online payment. Current functionality is User selects product and places in cart. User then processes payment 1. User is redirected to Payfast for payment. 2. When payment is done the user is returned to website but currently the web page displays the following message "We are not able to find your payment, but don't worry. You should receive an email confirming your payment in a few minutes. If the payment hasn't been confirmed you can contact us." A Sales Order is generated and then we need to create an Invoice etc and manually allocate payment, then send link via email to client. My requirement is to for the following to happen 1. Client pays on Payfast. 2. After successful payment client is returned to my website page with message"Thank you for your payment. Please click on the link below to download your file/s" 3 Provide link that will allow them to download file/s (If they select multiple files we need multiple links or bundle the files into a single link 4. If payment unsuccessful then message "Your payment has been unsuccessful. Please try later"