You are likely a new Paypal user or have set up your Paypal account or transaction as a business that sells physical products. Paypal may require that the payer takes extra action to confirm product shipment in order to release payment immediately.
If you receive a notification from Paypal inquiring about the transaction, like below, select SERVICE OR VIRTUAL PRODUCT to avoid having your payment put on hold. (DO NOT select Product.)
Regardless of the reason Paypal has your payment on hold, funds should be released by Paypal within 20 days. If you have any issues, please contact Paypal customer support.