4 Most Common Reasons you might see a spinning wheel or non-functioning PayPal popup:
-- Using Preview Link to test instead of live link... Solution: Always test using the live link url.
-- Config in Test mode, and PPv2 Integration is Live... Solution: they should both be the same.
-- Required Fields may not be filled in.. Solution: double check required fields are filled in. Pro Tip: Use this in conjunction with SCROLL TO ERROR add-on so if there a required field not filled in, the page will automatically scroll to the error.
-- Domain Name in use should also be added to the Domains area in CFProTools so the domain is whitelisted for usage.