most common reason for this is that the email address in your item listing doesnt match whats on your paypal account. go to your item listing and click sell similar item. find the decide how you'd like to be paid section and check the email address in the box.
If its wrong but the email address is used by you, add it to your paypal account. log into your account and click profile then update next to email. click add and type in the email address and click save. then go to your email inbox, find the confirmation email and click on the link inside. the payment should come threw in a few minutes. if not it may be the buyer cancelled it.
if its email is misspelt or no longer exists, contact your buyer and ask them to cancel first payment and resend to correct email address.
If the email is correct, you're email may be unconfirmed. log into your paypal acount. check the to do list on the right hand size. if there a option that says confirm email, click it and follow the instructions.
if none of these, then im stumped. phone customer services
