What test emails and phone numbers can I use in sandbox?
Fixed one-time codes can be assigned to designated test contacts only: US phone numbers with a 555 exchange (like +1 202 555 0142), and emails on example.com, example.net, example.org, or any domain ending in .test, .example, or .invalid.
Once set, every code sent to that contact uses your fixed value and nothing is actually delivered — while expiry, resend throttling, and attempt limits behave exactly as in production.