Once you've configured an integration for testing in our sandbox environment, you need to ensure that your test number is linked to the integration before messages will be delivered to your test phone number. Submitting test messages to a destination other than the test phone numbers registered, will return a simulated response which emulates what the response will look like in your system.
To double check that your sandbox integration is linked to your test number, open your integration from the SMS integrations page and select the ‘Phone numbers’ tab at the top of the page. Your test numbers will be listed here. Numbers with a green tick box are linked to your integration. Click on the tick box to link or unlink your test number to this integration. Test messages will only be delivered to a test phone if your number is linked here.