Docusign Powerforms Embed Success Status

I'm working on a PHP application that has multiple products which require signing from a customer before going for the product. I'm using powerforms link to embed them on my application (using iFrame).

They work fine. But the problem is I need to store the document signed status in my database.

The we can set a return URL in the Docusign Preferences Page. But that will be static and I won't have a clue of what product the user has selected.

References: Powerform Docs

You can use DocuSign Connect to receive real-time notifications of envelope events (for example, Envelope Completed). At a high-level, it works like this:

You login to DocuSign web console (as Admin) and create a Custom Connect Configuration. As part of creating this configuration, you'll specify the endpoint (http address) that you want Connect to send notifications to, and which events you want to be notified of.
You build a "listener" -- i.e., the web page that will receive the HTTP POST messages from DocuSign Connect, and process those messages.
When an Envelope or Recipient event occurs (for which you've enabled notifications in your DocuSign Connect Configuration), Connect will almost immediately send an HTTP POST to your listener. This message contains XML with info about the Envelope, Recipients, Documents, Fields, etc. You'll develop your listener such that it parses the XML message to determine Envelope status, data field values, etc. and then can respond appropriately within the context of your application (i.e., in your scenario, your listener would use the XML message from Connect to determine envelope status and which product(s) the user selected).

See this guide (http://www.docusign.com/sites/default/files/DocuSign_Connect_Service_Guide.pdf) and this page in the DocuSign Dev Center (http://www.docusign.com/developer-center/explore/connect) for more detailed information on configuring/using DocuSign Connect.

UPDATE - Using Custom Fields to populate unique Identifier for Envelope

Depending on the nature of your use case, you might need to use an "envelope custom field" to populate a unique identifier for each Envelope in the "create/send envelope" request, so that your listener application has a way of identifying the envelope when it receives a Connect message. (An 'envelope custom field' is simply a custom piece of metadata on an envelope.) Simply set the customFields property in your Create Envelope request, and populate a single textCustomFields item with the unique identifier. For example:

{
  "emailSubject": "Please sign this",
  "emailBlurb": "Please sign...thanks!",
  "customFields": {
        "textCustomFields": [
            {
                "value": "1234567",
                "required": "false",
                "show": "true",
                "name": "ProductId"
            }
        ]
    },
  "status": "sent"
  ...
}

See the REST API Guide (http://www.docusign.com/sites/default/files/REST_API_Guide_v2.pdf) for more detailed info about using Custom Envelope Fields.