I'm unable to configure PayPal Sandbox for the first time using "Manage API Credentials" in admin. The form in admin has these fields: API Username, API Password, API Signature, Merchant ID, PayPal E-Mail Address & Primary E-Mail Address. They don't match with the fields I can find from developer.PayPal.com (assuming i'm in the right place/page). In developer.paypal.com > My apps & Credentials -page I can find: Sandbox account, Client ID and Secret?