title: Paypal invoice integration
body: <p>I am new to paypal integration,</p>
  
  <p>Requirement (paypal USA): 
  Admin should be able to generate paypal invoice from website admin panel. As this is service invoice and charges will be different depending on client requirement.
  And User, from website client area can receive paypal invoice and pay it online.</p>
  
  <p>I ve read few documents of paypal api but couldn't decide which flow/API to use.</p>
  
  <p>Please suggest best way with least coding to integrate paypal with my website.</p>