Recurly offers three different site "modes" for you to utilize:
Sandbox mode is the default when you first sign up for a new Recurly site. This offers full Core functionality for testing. All transactions in Sandbox mode will route through the Recurly Test Gateway so that you can have a full trial of our service without using real credit cards. Sandbox sites are free forever, but may be subject to closure if inactive for more than 30 days.
Test transactions can be processed using test cards here: https://docs.recurly.com/docs/test
Certain 3rd party integrations are limited in the sandbox mode, but can be activated in Developer mode.
Development mode allows you more flexibility in testing. Like a sandbox site, no live transactions are processed. The difference is that while in Development mode you can connect to your payment gateway's sandbox environment and process test transactions. Any test transactions will be processed through your gateway's sandbox, and as a result must use the test cards/ tools provided by your payment gateway. This mode also allows you to connect AvaTax for testing.
Production mode is activated when you select and upgrade to a paid Recurly Plan. This offers you full, unlimited access to every feature of your selected plan, and begins processing live transactions. We do not recommend testing new setups or integrations in production mode. You can follow our Go Live Checklist to prepare for moving into Production mode.