Recipient has to confirm their email address with PayPal or register for a PayPal account to claim the money. Check if the payment was sent to correct email address to begin with. If email address is wrong, cancel the payment if a cancel button is present and resend to correct email address. Otherwise payment is returned unclaimed after 30 days if no cancel button is present and you may have to make another payment to the correct email address in the interim.
If recipient is from the US, they may have to “Accept the money” on the Summary page and verify some personal info to claim the money into their PayPal balance or withdraw immediately to a linked bank account.