Have you confirmed your email address and verified your paypal account?
Also have you had a paypal email to say you received funds?
Make sure its not a fake scam paypal email telling you to do things like send the item first as any funds would show in your balance even if on hold or pending.
Lastly check the email address the sender used and make sure there were no spelling errors or typos?
Advice is voluntary. Kudos / Solution appreciated.
