How to set Campaign/ProductID for a single PayPal button

If you want to pick the correct campaign for each PayPal button then simply add one line into PayPal button:

<input type="hidden" name="item_number" value="Product1">

Then go to your merchant panel > campaign > pick the campaign that you want to assign this product > edit details > Product ID matching > insert the product number into this campaign - in this case it's the Product1

Now every time this PayPal button is used for purchase, PAP4 will pick this campaign for calculating commissions etc..