Can I use API Signature and Certificate credentials at the same time?

No, you must choose either API Signature or API Certificate authentication. If you need to use both, you'll need to create two PayPal accounts.

Note: Some shopping carts require both API Signature and Certificate credentials. For example, Volusion offers a Payments Pro/Express Checkout solution that requires both methods. In that case, you’d need two PayPal accounts:

  • A parent API Certificate account for PayPal Pro  
  • A child API Signature account for Express Checkout

This is not a common issue, however, as most carts support both methods.

See also:
What are API Signature or Certificate credentials?