When you have set up a Payment Method as Paypal for your eCommerce store and might be you have faced the error of the Paypal gateway has rejected the request in Magento 2 or PHP Web application.
The error will be,
PayPal gateway has rejected the request. Security header is not valid (#10002: Security error) Continue reading “Error PayPal gateway has rejected request. Security header is not valid (#10002: Security error) PHP Magento 2.”