Yuansfer offers a sandbox environment to be used for testing the entire transaction flow and various use cases before deploying your service into a live environment.
Live and Sandbox environments have different base URL's, but all API names are the same. You can just use the dedicated secret token for live or sandbox transaction. Requests made with test mode credentials never hit the banking networks and incur no cost.
Payment Password on Cashier Page
You can download the Sandbox APK here. No account is needed.