How SMS verification works (and why codes don’t always arrive)

The basic flow

You enter a phone number; the service generates a one-time code, hands it to an SMS provider, and the provider routes it through the carrier network to the number’s line. You read the code and type it back in to prove you control the number.

Where it breaks down

Most “no code” problems happen before the message is ever sent:

• Line-type rejection: the service detects VOIP or a data-center number and declines to send.
• Reuse limits: the number has verified that service before and is rate-limited or blocked.
• Region mismatch: the service expects a number from a specific country and rejects others.
• Carrier filtering: the SMS is dropped or delayed in transit by a carrier’s spam filters.

Why a fixed window matters

One-time codes expire. A short-term verification gives the code a defined window to arrive — at Fetch SMS, 15 minutes — after which it is no longer valid. If nothing arrives in that window, the right behavior is to refund rather than charge for a non-delivery, which is exactly how the wallet credit works here.

Making the code land

Use a fresh, non-VOIP number in the region the service expects, and one that has not been used for that service before. That combination clears the line-type check, avoids reuse limits, and matches the region rule — the three things that most often stop a code.