How to set up a Paypal Sandbox environment in Magento 2.2.1 | Credentials Details.
Magento Commerce provides an on-boarding tool to configure PayPal Express Checkout accounts straight through the Magento Admin panel. This tool is available for 2.1.8 and later. To better support going live and testing PayPal payment methods, you can enable and configure your PayPal Express Checkout account for sandbox or production accounts.
You can configure either the sandbox or production account in every environment:
For Integration and Staging environments, we recommend setting Sandbox credentials. For your Production environment, you can set Sandbox credentials for initial testing, then replace with live production credentials for a launched store.