There are a few things you can check:
1. Perhaps there is a delay while payment is being processed in which case download will not be delivered until payment has cleared. Check you PayPal transaction to see if this is the issue.
2. Make sure your PayPal Instant Payment Notifications (IPN) have be configured correctly. Make sure in your PayPal account IPN is not disabled. You need to log into your PayPal account and go to the Instant payment Notification settings under your Profile. Once there, set the IPN to "Enabled" and input https://www.payloadz.com/pay/index.asp as the URL and submit the changes.
3. Please make sure you are using "Buy Now" or "Add To Cart" buttons on your website that are generated by Payloadz.
Please check these and there is still a problem please contact Payloadz Support and provide txn id, buyer email, product name, date of purchase etc. this will help us to resolve any issues.