10002 error

Keep getting this error:

SetExpressCheckout API call failed.

Error Code: 10002
Error Severity Code: Error
Short Error Message: Security error
Detailed Error Message: Security header is not valid User IP: 81.135.101.63

Any idea what it means and how I can fix?

Thanks

Derek

https://www.ads-software.com/plugins/paypal-for-woocommerce/