PayPal
The Paypal settings for Sandbox & Live, you can go directly to their SandBox Page. Also if you have any doubts, you can check their Documentation through this page.
2Checkout
The 2Checkout settings for Sandbox & Live, you can go directly through their Sandbox Page. Also if you have any doubts, you can check their Documentation through this page.
Stripe
The Stripe settings for Sandbox & Live, you’ll find the API and Secret Key through your Stripe Dashboard. You can read Stripe Documentation for more details here.