The app says my number cannot be used

Some apps refuse certain numbers outright, before sending any code. Many never say so: they show "code sent" and nothing arrives, which looks exactly like a slow code.

Either way, the way out is the same. Three minutes after you get the number, “No code?” opens on it. Tap it, then choose Rejected if the app would not accept the number, or Nothing arrived if it took the number but no code came. Both move you to a different number at no extra cost.

You can do that twice. If the second replacement does not work either, the activation is refunded automatically.