What funding source are you using? PayPal balance or card? Any error message that comes up when you try send the money? What country is the person you're sending the money registered in? What amount did you send? You would need provide more information, but most likely you would need to contact customer support. It could be security system that blocks your payment. It could be you reached your sending limit and in this case need to link and confirm a card. It could be your friend you sending to is not able to receive the money if their PayPal country does not allow them to receive personal payments or that you or receiver have a limit on the PayPal account.