This is difficult, not because of technology, but because of the variety of decisions in the field of commerce and the open nature of human choice.
It looks like you created two vital components for this job: the ability to identify registered merchants and the ability to host a script on your web page.
I need a third component, I think; either a consistent interface for this script (as soon as a commercial transaction is completed or fails, pass the object with statuses back to your script through a specific triggered event) or fully familiarize yourself with the events for the seller’s website that you can code.
Encoding the unknown will take a lot of time and effort, since you will need to learn each transaction solution for outlets and how to capture transaction data. It will be ... a long way, and I do not think it will be very successful.
If the seller’s site is ready, it can trigger an event that your script will listen to and transmit transaction data through, which will allow your script to go through AJAX to the wait tracking page to record the results. This is easiest in terms of reaching an agreement and for working from your specified starting point. jQuery is a great library to hook it all up, and there are other options.
Part of the tracking will go through the token, which should be transferred through the transaction and transferred back generated by your site to a click on the seller’s website and transferred from there. After you return the token, you can compare it with the database of transaction tokens to find out which event has which result and fill in the corresponding fields from the received data.
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