Popunder tracking is challenging because users often close those ads quickly or complete actions much later on different devices. Standard tracking pixels miss a lot of conversions from popunder traffic since the customer journey is more complex than regular display ads. I was losing money on popunder campaigns because I couldn't see which ones actually converted. Started using free conversion tracking tools that capture more data points and help connect the dots between popunder clicks and actual sales. Without proper attribution you're basically gambling with your popunder ad budget