Integrating Paypal to my Gridmarket Site

So I have been working on a website where I can market and sell my children’s clothing range globally and am SO close to getting it where it needs to be but when I test the payment system it just sends the message “There was a problem connecting to PayPal to setup your purchase. Please try again. 10002 – Security error – Security header is not valid” after I have entered all my shipping information. I have created my business paypal account and entered my api username, password and signature into the required fields in store settings but nothing more than this. I’m thinking that there is some other step in the set up process that I am missing and wondering if someone could help as soon as possible as my business partner accidentally started advertising the website so I have customers visiting the site and trying to make purchases when the system doesnt work which obviously doesnt make us look very good :slight_frown: Any help would be appreciated!

Kindest Regards, Ashleigh