I followed your instructions as closely as possible.
I used Paypal LIVE.
I located the API Usernanme, secret key, and ID signature keys, on my PayPal buissnes account. The PayPal logo appears in my cart checkout but when I click it, I get an error message:
Security Header is not valid Error code 10002…
Have you an idea concerning this problem ? I read the related topics in your on line documentation … but it not very helpfull for me . Thank’s