If you want to test PayPal with your shopping cart, you should use the sandbox. To set this up, use the following steps from PayPal.

  1. Log in at https://developer.paypal.com/.
  2. Click Test Accounts.
  3. Select the test account.
  4. Click Enter Sandbox Test Site.
  5. Log in and click Profile.
  6. In the Account Information column, click the API Access link.
  7. Click the Request API Credentials link.
  8. Select the API SSL client-side certificate radio button.
  9. Select the checkbox next to I agree to the API Certificate Terms of Use and terms incorporated therein.
  10. Click Submit.
  11. Click Download Certificate. Note the API username and API password; you need them later with the certificate to make an API call.