To have a proper functioning PayPal Payout running on your site that helps disburse vendor’s payments, go to the PayPal Payout tab under Payments and enter the Client ID and Secret obtained from PayPal.
For new PayPal accounts, it is mandatory as per PayPal guidelines, to have asynchronous mode enabled as the synchronous mode is deprecated, while for older accounts both synchronous and asynchronous modes are available and hence, we’ve left it up to you to decide.
In a brief perspective: In Synchronous mode, PayPal would immediately pay the vendor without checking for any payment related risk factors and return the payout status instantly while for Asynchronous mode PayPal checks for all the risk factors involved and then proceeds with the payment later sending you the payout status. Also, in Synchronous mode, Paypal handles one payout at a time while Asynchronous mode handles multiple individual payouts in one API call.For more details read this document. To do a quick test payment before going live using PayPal sandbox check the box for Enable Test Mode.