I'm using:
$email = $_REQUEST['payer_email'];

to get the payer's email address after they had made their payment and redirected back to my website.
However it doesn't work, i.e. $_REQUEST returns nothing.

Further , the code I'm using works fine in the sandbox and also when the user makes a credit card payment through paypal (without logging into their account), that is $_REQUEST['payer_email'] returns the correct payer email address. But it does not work when a payer logs into their account to make the payment.

What am I doing wrong?