Sandbox
Test mode: no real money moves.
Use a test key
Create an ek_test_ key with payments:write and payments:read in your workspace. Live keys are rejected by the tester.
Try the API
Receipt scenarios
Open the returned payment_url, then run receipt scenarios from the Sandbox tools in your workspace. Test a valid receipt, an amount mismatch, a duplicate and a delayed receipt.
Alert testing and replay stay in the authorized workspace. The portal does not simulate a successful delivery.