It is not easy to integrate Nanacast with Post Affiliate Pro so you should consider a help of a professional.
Post Affiliate Pro has a plugin for handling Nanacast notifications so you can track order details, coupon and customer details as well.
Create a custom field
Navigate to your Nanacast admin panel and then to Manage > Products (or Manage > Memberships).
For each of your products you will have to repeat these steps!
Create a new custom field - click the link 'Notifications/Custom Fields' then click the link 'Add A New Custom Field That You Define'. Set the type to Hidden Field, name it as 'PAPVisitorId' and that's it, save it.
Set notification URL
When still in the section 'Notifications/Custom Fields' - check the 'Activate Advanced Outgoing API' checkbox and enter your plugin URL:
Save your settings.
Order page integration
Visit the actual product payment link (you can get it in section 'Create Button') and check the page source code with a code inspector to see what ID is set for your custom input field (u_custom_1) - if you have more custom fields, then check the one you added for 'PAPVisitorId'. Save its ID, you will need it.
Navigate to 'Edit Pricing/Delivery' and add this script into 'Customized Credit Card Order Page' section of 'Secure Checkout Page Settings' (in case you already have your own code there, then find credit_card_order_form variable there and replace it with the following):
As you can see, there is a place for the 'field ID from the sourcecode'. Replace it based on yours. Make sure the https://URL_TO_PostAffiliatePro/scripts/salejs.php is available because of the SSL certificate.
Activate the plugin
The last step is to activate the Nanacast plugin. Navigate to your merchant panel and activate it. In the plugin configuration section set the custom ID number. All your products have to use the same custom field number (e.g. 1 stands for the first custom field) for tracking purposes.
If you want to track every product to a different campaign (per product tracking) then use 'Advanced API ID' value displayed next to the product name (in Product Overview section).
Do not forget to integrate your site with the click tracking code to make the sale tracking working.