To enable the PayPal recurring payment method in nopCommerce please follow these steps:

• Login to application with Admin credentials.
• Go to Administration section.
• Go to Configuration > Payment > Payment Methods.
• Click the Edit link on PayPal Direct payment method.
• Click Configuration tab. 
• If you are going to use Sandbox (test) account, check the Use Sandbox checkbox or leave it unchecked if not.
• Select the transaction mode depending on the requirement. If you want to just authorize the credit card, then select Authorize. If you want to have actual payment instantly then go for Authorize And Capture.
• Enter the Transaction key and Login ID which you get from PayPal account.
• Click Save.
• In the System Info tab check the Active checkbox to make the payment method active, accept payment using Credit Cards.