1) Click on 'PayPal Checkout' button and see the experience.
2) If you get any Firewall warning, add rule to the Firewall to allow incoming connections for your application.
3) Try Checkout with PayPal using a buyer sandbox account provided on this page. And you're done! Or you can use Proceed to Checkout for Express Checkout Mark flow.
4) The sample code uses default sandbox credentials which are set in 'application.properties'. You can create your own credentials by creating PayPal Seller and Buyer accounts on Sandbox here.
5) Make following changes in 'application.properties':
- If using your own Sandbox seller account, update CLIENT_ID and SECRET values with your sandbox credentials
- IS_APPLICATION_IN_SANDBOX: Kept true for working with Sandbox, it will be false for live.