I'm stuck in a small issue and is unable to fix it.
I'm using PayPal IPN for payments. All things are working correct, except when browser is re-directed to my site after successful payment, I'm unable to verify the payment. I'm using PayPal curl API and have copied the code from PayPal website. Also I've enabled IPN in merchant account.
Your problem isn't clear. PayPal should send data to the URL pointed to by your account's IPN setting. That URL should point to a script that simply records the results of the PayPal transaction so you can confirm the details. Once the PayPal transaction is complete, the user should be redirected to a different URL - usually a Thank-you page. I wouldn't absolutely count on the IPN script being called in time for the Thank-you page to be able to determine if the transaction was successful, but it usually is.