I'm about to create a PayPal payment gateway for donations on my website, it goes fine with the sandbox account, but when I turn to the live mode, it does not end well. The PayPal check-out window pop and disappear immediately in a live mode before even showing anything in that window. The only thing I changed on the live mode is the post URL which I replaced "api-m.sandbox." with "api-m." behind this "paypal.com"