Paypal's "Security header is not valid"
- by Paypal
I'm implementing the Express Checkout?
I have no problem with the first two steps:SetExpressCheckout and GetExpressCheckout,but met the "Security header is not valid" at DoExpressCheckout.
The API credentials are the same!
I've fixed it by changing the $environment to live in DoExpressCheckout.(The difference is that it'll use https://api.sandbox.paypal.com/nvp/ instead of https://api-3t.$environment.paypal.com/nvp)
But why?
Is there something wrong with https://api-3t.$environment.paypal.com/nvp?