Getting Error #10002. Security error. Security header is not valid. - Paypal Sandbox

The site is secured as SSL and Paypal Info are setup on the account details. Unfortunately, we are getting this error when we try the paypal pro form in sandbox option: Error #10002. Security error. Security header is not valid.

Any help is appreciated. Thank you!

Don’t use Paypal sandbox. It’s buggy, as you find…