Test mode

Test keys (i100x_test_…) see only test objects. A test practice invite (pi_test_…) gets the same request checks as a live one — including the country rule and the Idempotency-Key — and its url opens a test page, /test/practice/{token}, with Simulate sign-up (sends practice.signed_up to your test webhooks), Simulate plan created and Simulate a practice session (these only change your test stats). Test stats are exact ("rounded": false) and every answer carries "livemode": false.

A live key naming a test object, or a test key naming a live one, answers 403 TEST_MODE_ONLY. Live events never reach an endpoint created with a test key.