**The App Says the Number Is Invalid — How to Fix It** > A number rejected before dialling is nearly always a missing country code or a trunk zero left in. The four ways a phone number goes wrong, and how to write it… Source: https://telvio.app/help/number-not-accepted/ · updated: 2026-09-04 1. [Home](https://telvio.app/) 2. [Help](https://telvio.app/help/) 3. The number is not accepted Numbers # The number is not accepted A number rejected before the call is placed has failed a format check, not a network. There are four ways that happens and they are quick to tell apart. - Four failure modes - Free validator in the browser - Works for any country Write it this way A number has to be in international form: **+**, then the country code, then the national number with any leading trunk zero removed. A London number written locally as *020 7946 0958* is **+44 20 7946 0958**. A Delhi number written locally as *011 2345 6789* is **+91 11 2345 6789**. The leading zero is a domestic dialling instruction, not part of the number, and leaving it in is the single most common reason a number is rejected. Paste the number into the [phone number validator](https://telvio.app/tools/phone-number-validator/) to see which country it belongs to, whether the length matches that country's numbering plan, and what the correct international form is. It runs in the browser and nothing is uploaded. ## The four ways a phone number goes wrong 1. 1 ### The trunk prefix was left in Most countries put a digit — usually 0, sometimes 1 or 8 — in front of a number dialled domestically. It tells the local network that a long-distance call follows, and it has no meaning internationally. *+44 020 7946 0958* is not a longer version of a valid number; it is an invalid one. Remove the zero that sits immediately after the country code. 2. 2 ### The country code is missing A number copied from a local website, a local business card or a contact saved while you lived in that country has no country code. It looks complete and is unusable from anywhere else. If the digits match a plausible national number but there is no dial code in front, this is what happened — find out the country and prefix it. 3. 3 ### A digit is missing or duplicated Numbering plans are strict about length. A country that issues nine-digit numbers does not have an eight-digit one hiding somewhere, so a national part that is one digit short is a typo rather than an exception. The validator checks length per country, which is what makes this catchable before you dial. 4. 4 ### The number was written for a different system *00* in place of *+* is fine and is handled. Letters are not: 1-800-FLOWERS has to be converted to digits before anything will dial it. Extensions appended after a comma, a hash or a semicolon are a phone convention rather than part of the number — dial the main number and enter the extension on the in-call keypad once the system answers. ## Why the check happens before the call rather than after Checking a number's shape locally costs nothing and takes no time. Attempting a call to a malformed number costs a round trip to the network, produces an error that is often unhelpfully generic, and occasionally connects to something you did not intend — a number one digit short is not necessarily unassigned, and in a few countries it is a chargeable service. So the app validates first. It checks that the number begins with a real country code, that the national part is a plausible length for that country, and — where a country publishes distinct ranges — whether the leading digits mark it as mobile or fixed. That catches the overwhelming majority of numbers that are wrong before any money or time is spent. What that check cannot do is tell you whether the line is in service, who owns it, or whether it has been ported to a different operator. Nothing that runs on a phone can. Establishing that a number is live requires either placing a call or querying the operator's own database through a paid lookup, and any tool that shows a green tick labelled “active” without doing one of those is showing you a syntactic result with a misleading label attached. ## Numbers that are correctly formatted and still refused - **Premium-rate and shared-cost ranges** are blocked. Their price is set by the number's owner rather than by the network, so no service can quote a rate for them in advance. - **Short codes and service numbers** — three, four or five digits — exist only inside their own country's network and have no international form to dial from outside it. - **Emergency numbers** cannot be reached, deliberately. An internet call carries no verified location, so an emergency operator would not know where to send help. Use your phone's own dialler; see [emergency calls](https://telvio.app/legal/emergency-calls/). - **Destinations we do not serve.** Some countries and some number ranges within served countries have no route, and the app declines rather than connecting at a price it cannot promise. [What that means](https://telvio.app/help/destination-not-available/) is a separate page. - **Numbers behind a switchboard that needs an extension** connect to the switchboard fine. The extension goes in afterwards, on the keypad. ## Storing numbers so this stops happening The habit that prevents all of this is storing every number in international form, including the ones in your own country. It costs nothing while you are at home and it is the difference between a contact list that works abroad and one that does not. The international form is called E.164, after the ITU standard that defines it: a plus sign, one to three digits of country code, and up to fifteen digits in total, with no spaces, brackets or punctuation. Written that way a number means the same thing from anywhere in the world, dials directly from anywhere, and deduplicates correctly when two apps sync the same contact. Phones display stored numbers in whatever local format the reader expects, so there is no readability cost. The only work is a one-time pass through your contacts, and the moment it pays off is the first time you try to call home from another country. ## Why a number that works locally fails from an app This trips up almost everybody once, and the explanation makes the rule easy to remember rather than easy to forget. When you dial from your phone's own dialler, the call is placed on a mobile network that knows which country your SIM is registered in and which country you are physically standing in. That context is what lets a domestic form work: the network reads a leading zero as an instruction rather than as a digit, and fills in the country for you. An internet call has no such context. It is placed from a data connection, not from a country, and there is nothing to infer the missing country code from. So the number has to carry everything: the plus sign that marks it as international, the country code, and the national number with the domestic instruction removed. That is not a limitation of the app; it is what an international number is. The practical habit that removes the problem permanently is to store every number in your contacts in international form, including the ones at home. Phones display them in the local format anyway, so there is no readability cost, and the day you try to call home from another country you will not have to work out the country code under pressure. ## Bottom line Write the number as a plus sign, the country code, then the national number with the leading trunk zero removed. That fixes most rejections on the first attempt. The four failure modes are: trunk zero left in, country code missing, a digit wrong, and formatting borrowed from another system. The [validator](https://telvio.app/tools/phone-number-validator/) identifies which one you have. A correctly formatted number can still be refused if it is premium rate, a short code, an emergency number, or in a destination we do not serve — none of which is a formatting problem. ## Frequently asked questions How do I write a phone number for international dialling? Use a plus sign, the country code, then the national number without any leading trunk zero. A London number written locally as 020 7946 0958 becomes +44 20 7946 0958. This form is called E.164 and it means the same thing from anywhere in the world. Do I remove the 0 when dialling internationally? Yes. The leading 0 in most countries is a domestic dialling instruction and is not part of the number. Leaving it in after the country code produces an invalid number and is the most common single reason an international call fails. Can I use 00 instead of +? Yes, 00 is the international exit code in most of the world and the app handles it. The plus sign is preferable because it works from every country including the ones that use a different exit code, such as 011 in the United States and Canada. Why is a number rejected even though it is correct? A correctly formatted number can still be refused if it is a premium-rate or shared-cost range, a national short code with no international form, an emergency number, or a destination the service does not have a route to. None of those is a formatting problem and none is fixable by rewriting the number. Can the app tell me whether a number is active? No, and nothing that runs on a phone can. Checking that a line is in service requires placing a call or querying the operator's own database through a paid lookup service. The validator confirms that a number is well-formed and plausible for its country, which is a different and much cheaper claim. How do I dial an extension? Dial the main number, wait for the switchboard to answer, then enter the extension on the in-call keypad. Extensions appended to the number itself after a comma or a hash are a convention some phones understand and the telephone network does not. Why does the same number work from my phone's dialler but not here? The built-in dialler is on the mobile network and can use the domestic form of a number, including the trunk zero, because the network knows which country you are in. An internet call is placed from no particular country, so it needs the full international form with the country code and no trunk prefix. ## Related answers - [The person you call sees a number they do not recognise](https://telvio.app/help/they-see-an-unknown-number/) - [You paid and the credit has not appeared](https://telvio.app/help/credit-did-not-arrive/) - [Refunds, and charges you did not expect](https://telvio.app/help/refunds-and-charges/) - [The free minute did not work](https://telvio.app/help/free-minute-did-not-apply/) ## Still stuck? Write to us with the date, the time and your time zone, and say what you saw. A person reads every message and we aim to reply within 24 hours. 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