You can use Product ID to force the affiliate system to choose a particular campaign.
Whenever a visitor clicks an affiliate banner or link, the referral information is stored into the cookie. This includes also the campaign of the banner/link clicked.
Now, when the sale is accomplished, the affiliate system generates a commission according to the campaign that was stored in the cookie, which may not be the campaign where this product should belong to. If you want to assign your products to particular campaigns, you should use the Product ID parameter and define the particular product ids in the particular campaigns.
How to force choosing campaign by product ID
You have to add product ID parameter in the sale tracking script, for example:
var sale = PostAffTracker.createSale();
Hidden image (pixel) tracking code would look like:
<img src="http://URL_TO_PAP/scripts/sale.php?AccountId=default1&TotalCost=120.50&OrderID=ORD_12345XYZ&ProductID=PRODUCTX" width="1" height="1" >
Both tracking codes above would pass the product ID parameter with value PRODUCTX to Post Affiliate Pro (Post Affiliate Network).
In case of using PayPal buttons, the product ID goes to the item_number field.
If you are going to use a hosted PayPal button (saved at PayPal), then whatever you put into the "Item ID" field when configuring the button in your PayPal account, then it will be used as the value of item_number field in PayPal's notification (IPN):
In case of using a shopping cart, the creator of the shopping cart should be able to tell you by what variable you can obtain the unique id of your product.
Now you need to set up this product ID in the campaign. In the Campaign manager, click the (Edit) button to edit the campaign an in the Edit details tab you have the 'Product IDs' field to define the Product ID(s) there. You can enter more product IDs separated by comma.
Now every time a sale with the given product ID is registered, the commission will belong to this campaign.
NOTE: It is not advised to use the same product id in more campaigns. If you do, the system will look for the product ID first in private campaigns, then in public with manual approval campaigns and only then in regular public campaigns. If the same ID is found in multiple campaigns of the same type (private, manual approval, public) then the campaign is selected randomly.
There is an example here how to track each item of a purchase as a separate transaction: