If you have PayPal purchases that are not showing up as conversions in Spring Metrics, it probably means that people are not clicking a link to return to your store after they purchase.
You can set up your PayPal account to automatically redirect people back to your site after the purchase is complete. To do this, login to your PayPal account, and click the Profile subtab under My Account:
Click on My Selling Tools. In the Selling online section, click the Update link for Website preferences:
Select On for the Auto Return, and enter your site's conversion URL in the Return URL text box (make sure that you enter the same URL that is being used to track conversions in Spring Metrics):
Once this URL is in place, PayPal customers will be redirected to the "thank-you" page on your site, which will cause conversions to appear in Spring Metrics.