https://api.plexypay.com/v2, for example /v2/payments or /v2/sessions. The API key you send determines the mode. Do not switch Plexy SDK environment values away from live/APSE.live-apse; Flutter uses Environment.apse; Android uses Environment.APSE; iOS uses Environment.liveApse. These values stay live/APSE for both test and production runs.x-api-key from the merchant backend to run simulated transactions. No money is moved, and results are deterministic based on the payment data you submit.x-api-key to your live APSE key only after the integration is verified and the account is approved for production.clientKey and backend x-api-key must belong to the same merchant account and mode. For test transactions, use the test key pair. For production APSE traffic, use the live/APSE key pair.