The usual causes at a glance
A missing code is rarely random. Work through these causes before you request another one: repeated requests can trigger limits and make things slower.
| Cause | What you may notice | What to do |
|---|---|---|
| The service refuses this kind of number | No SMS at all, or an error about the number | Use a number type the service accepts, or another sign-in method |
| The code went another way | A prompt, a call or an in-app message instead of an SMS | Check the service’s app, or pick the SMS option if there is one |
| Too many attempts | A message asking you to wait | Wait, then use only the newest code |
| Wrong number format | Nothing arrives | Re-enter the number with + and the country code |
| Location or risk signals | Codes delayed or held back in some places | Try again later, or use another verification method |
| The number was used before | Someone else’s account, or “Activation failed” | Stop; never use another person’s account |
The service doesn’t accept this kind of number
Several services say plainly that internet-based or virtual numbers can’t be used. Viber says internet-based phone numbers cannot be used to register. LINE says virtual phone numbers can’t be used. Microsoft says VoIP numbers cannot be added as a way to sign in or get verification codes. Telegram connects accounts only to mobile numbers, not landlines.
In these cases the service may simply never send an SMS, and asking again won’t change the answer. For background: the US standards body NIST once told verifiers not to use VoIP numbers for out-of-band authentication (SP 800-63B, revision 3). Its July 2025 revision removed that prohibition, but still asks verifiers to weigh risk signals such as a SIM change or number porting.
The code was sent another way
Not every code is an SMS. Telegram may send a login code inside the Telegram app. Viber mostly activates through an automated phone call, a Flash Call, where the code is the last four digits of the calling number. Google may send a prompt to a signed-in device instead of a text. LINE offers to call you instead.
A DualLine one-time number shows codes that arrive by SMS. A code sent by call or inside another app won’t appear in DualLine.
You hit a limit on attempts
Services limit repeated requests to fight spam. Viber gives you three tries to enter a code, then asks you to wait 24 hours before requesting another. LINE may ask you to wait a number of days and says those restrictions can’t be lifted. Microsoft warns that excessive or repetitive requests can get you blocked. Google says that if you requested several codes, only the newest one works.
Wait before you try again, and always use the most recent code.
The number was entered in the wrong format
Telegram asks for the international format: a plus sign, the country code, then the number. Viber detects the country code automatically, which can be wrong, and asks you to enter the number without the leading zero. Check the country code before you request a code.
Location, network and risk signals
Google says delivery speed and availability vary by location and provider, and that if something about your sign-in looks different, such as your location, you might not get a code by text message. Microsoft says SMS can be limited or temporarily unavailable in some regions, and that it may not deliver codes when there is heavy compromised traffic from your location.
The number was used before
Phone numbers get reused. Viber says “Activation failed” can mean you inherited a recycled number that was flagged earlier. LINE may show a previous owner’s account on a “Welcome back” screen. Princeton researchers who obtained 200 recycled numbers found that 19 still received security codes meant for previous owners within a week.
If a service shows you someone else’s account, it isn’t yours: don’t continue. On LINE, choose the option that says it isn’t you.
If you’re waiting on your own phone
On your own SIM, check whether your phone blocks texts from unknown or international senders. Microsoft names this as a cause, and LINE says its codes may come from several domestic and international numbers, so blocking or spam filters can stop them.
How DualLine handles a code that never arrives
With a DualLine one-time code, the credit is taken when you place the order and the number is held for one code. The app shows how much time is left; the window is about 15 minutes for most services.
If no code arrives in that window, the full credit comes back to your DualLine balance automatically, at the latest 24 hours after the order. It returns as DualLine credit, not to a card or through the app store. If a code does arrive, the order is complete and nothing is returned, even if the service then refuses the number.
Each order receives one code, so a new attempt is a new order. Check the causes above first; the app also lets you try another service or country.
| Outcome | Your credit |
|---|---|
| No number could be issued | Not charged, or returned in the same step |
| A number was issued but no code arrived | Returned in full to your DualLine balance, automatically |
| A code arrived | Used; the order is complete |
| A code arrived, then the service refused the number | Not returned |
Your take-away checklist
- Confirm the service accepts this kind of number.
- Check whether the code came in an app, by call or as a prompt.
- Use the international format and the right country code.
- Wait out any attempt limit, then use only the newest code.
- Stop if you see someone else’s account.
- In DualLine, keep the order open until the window closes.
Common questions
How long should I wait for the code?
In DualLine the window is about 15 minutes for most services, and the app shows the time left. Requesting several codes in a row can work against you: some services only accept the newest one.
Do I pay if the code never comes?
The credit is taken when you place the order. If no code arrives, it comes back to your DualLine balance automatically, at the latest after 24 hours.
I received the code, but the service still refused the number. Why?
Receiving a code and being accepted are separate steps, and the service decides the second one. Once a code has arrived, the order is complete and the credit isn’t returned.
Can DualLine resend the code?
Each order receives one code. To try again, place a new order after checking the causes on this page.
Sources and support
Each cause on this page comes from the service’s own help pages or from the cited research. What happens to your credit is shown on the DualLine order screen.
- Viber Help — Solve activation and registration issues
- Viber Help — Set up Viber on your phone
- LINE Help — Creating a new LINE account
- LINE Help — I can’t verify my phone number
- LINE Help — Welcome back screen with someone else’s name
- Microsoft Support — Troubleshoot verification code issues
- Google Account Help — Fix common issues with 2-Step Verification
- Telegram FAQ — Login codes
- NIST SP 800-63B (revision 3)
- NIST SP 800-63B-4
- Princeton CITP — Phone number recycling risks