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.
Always on development, use the appropriate payment gateway as Sandbox. Whether you choose the Live payment, all payments will be deducted from your real money. To avoid any a headache, use always the Sandbox. Just change to Live when you finish your tests and are ready to go public to start getting profits with your directory.