This is great plugin, really easy to use.
I've set up Paypal for my client using the PayPal ExpressCheckout Settings with the API credentials. and when I go through to test payment it comes up with an error.
There was a problem connecting to PayPal to setup your purchase. Please try again. 10002 - Security error - Security header is not valid
The checkout process works fine, until you get up to the actual checkout stage - first there is a page with no content which says "Continue Checkout" and then that error comes up.
I've double checked the API credentials and they are definitely correct... so how do I fix this?