You verify the customer. But do you verify their number?

One-time passwords have become a familiar part of the customer journey.

A customer creates an account, signs in, resets a password or confirms an action. They enter their mobile number, a one-time password is generated, and an SMS is sent.

It appears simple.

But an assumption is hidden in that process: before you use an OTP to verify the customer, how much do you actually know about the phone number you are sending it to?

For many businesses, the answer is surprisingly little.

The number may have passed a basic formatting check. It may look like a legitimate mobile number. It may even already sit within the customer record. However, none of that necessarily tells you whether the number is a suitable destination for the SMS you are about to send. When the OTP sits between your customer and whatever they are trying to do next, that matters.

Think about a typical SMS OTP process.

• Customer enters mobile number
• OTP generated
• SMS sent
• Customer receives code
• Customer continues

Most attention naturally goes to the OTP itself.

Was the code generated correctly? How long should it remain valid? How many attempts should the customer have? When should another code be generated?

All important questions.

But there is another question that comes before all of them:

Is the number you're about to use a viable mobile number?

If you haven't checked, your OTP process may be starting with an assumption rather than a fact.

That number could have been mistyped. It could be incorrectly formatted. It could be inactive or disconnected. It could be a different type of number than you expected. Or, there could simply be information about the number that your customer journey would benefit from knowing before you try to contact it.

The problem is that if you don't perform that check beforehand, you often don't discover the issue until after you have tried to send the OTP.

By then, the customer is already waiting.

There is a big difference between a marketing SMS not reaching someone and an OTP not reaching them.

If the customer is waiting for a one-time password, the SMS is usually standing between them and an action they really want to complete, whether that’s creating an account, signing in or confirming a purchase.

The OTP isn't just a message. It's part of the journey. And, when it doesn't arrive, the journey stops. The reason doesn't particularly matter to the customer, they won't know whether their number was entered incorrectly, whether there was a delivery issue or whether something else has gone wrong.

All they experience is “I haven't received my code.”

What happens next can create a much bigger business problem.

At low volumes, an unsuccessful OTP send might look insignificant.

At scale, the consequences begin to add up.

1. You can spend money attempting to contact unusable numbers

Every OTP sent uses messaging resources.

If a business sends an SMS before confirming the destination is valid, it can end up paying to attempt delivery to numbers that should have been challenged earlier in the journey.

One failed attempt might not matter, however, thousands, hundreds of thousands or millions of unnecessary attempts are a different story, and the cost isn't always limited to the first message.

2. Customers request another code

What does somebody do when an OTP doesn't arrive?

Usually, they press: Resend code.

Businesses now make another messaging attempt to the same number, potentially without anything having changed.

And then perhaps another.

The underlying problem remains unresolved because the process is trying the same thing again rather than asking a more useful question: is there something wrong with the number we're sending to?

3. Customer frustration starts almost immediately

An OTP journey creates an expectation: the customer enters their number and expects a code within seconds. When that doesn't happen, uncertainty starts.

Should they wait? Request another code? Check their phone? Go back? Re-enter the number? Contact support?

A process designed to make access simple can quickly become an immediate source of friction as the customer is usually trying to do something at that exact moment.

4. Your support team can inherit the problem

“My verification code hasn't arrived.”

It is a simple and highly popular customer complaint, but diagnosing it can be much less simple.

Support may need to check the account, confirm the number, ask the customer to try again and potentially escalate the problem.

What began as an unchecked piece of customer data can become a customer service interaction. Multiplied across a large organisation, poor contact data can create operational work far beyond the cost of the original SMS.

5. Customers can abandon the journey

Not everybody contacts support. Some simply stay silent and leave.

If an OTP is required to complete registration, access an account or continue a transaction, failure at that point can mean the customer doesn't complete what they came to do.

The business may see an abandoned registration or an incomplete customer journey. The business won’t see the initial problem, and how quickly that sale could have been saved by a simple phone number verification check.

6. The bad data can stay with you

Another consequence, which is easy to miss is that that incorrect information stays within your database, remaining inside the customer journey.

The simplest way to make this process smarter is to introduce a number verification step before the OTP is generated and sent.

The journey becomes:

• Customer enters number
• Number checked
• Decision made
• OTP generated
• SMS sent

That additional check gives the business an opportunity to identify problems while the customer is still in the journey and can act on them.

If the number checks out, they will continue.

If something doesn't look right, the business can decide how the journey should respond, which may mean asking the customer to check the number they've entered, provide another number or follow an alternative process.

The important difference is that the business now has information before committing to the send.

Most digital forms already perform some kind of phone number validation, which is useful. But it is important to understand what that check actually tells you.

A basic validation rule might establish that a number is in the expected format, contains the right number of digits or appears to match a recognised numbering structure.

That helps catch obvious errors.

But a number looking right doesn't automatically mean it is a good destination for an OTP.

This is where deeper number verification and network intelligence can provide more useful information about the number being presented.

The distinction is simple:

Validation asks: “Does this look like a legitimate phone number?”

Verification asks: “What can we determine about this number before we try to use it?”

For an OTP journey, that additional information can be valuable.

Consider these two approaches.

Without number verification

1. Customer enters number

2. OTP generated

3. SMS sent

4. Wait to see what happens

5. Code doesn't arrive

6. Customer requests another OTP

7. Support, frustration or abandonment

The messaging attempt becomes the point at which the business discovers a problem.

With number verification

1. Customer enters number

2. Number is checked

3. Suitable number?

Yes: continue with OTP

Problem identified: challenge or correct the number

4. OTP generated

5. SMS sent

The difference isn't complicated. You're simply moving the question “Can we use this number?” earlier in the process.

It's important to be clear about the role number verification plays.

Verifying information about a phone number is not the same thing as authenticating the person holding the device.

And it doesn't replace whatever authentication, security or fraud controls your organisation has chosen to use.

Instead, it strengthens the process around the number itself. Think of the two steps as answering different questions.

Number verification:

What can we determine about the phone number we're being asked to contact?

OTP:

Can the customer complete the verification step associated with that number?

The role of number intelligence isn't to promise that every customer is genuine.

It's to help businesses make better-informed decisions about the contact information they have been given.

Acudo helps businesses check phone numbers before relying on them for important customer communications.

Rather than treating every entered number as equally trustworthy or usable, organisations can use phone number intelligence within the customer journey to understand more about the number before deciding what to do next.

For an OTP process, this creates a simple principle:

Verify, then send.

Verification can happen in real time, while the customer is still completing the journey. Your business remains in control of what happens next.

A number that meets your requirements can proceed through to the OTP send.

A number that doesn't can be handled according to your own rules, whether that's asking for a correction, gathering additional information or using another process.

Acudo isn't replacing your authentication journey; we help you make sure the mobile number entering that journey deserves to be there.

Businesses often have enormous customer databases containing mobile numbers, but having a number is not the same as knowing you can successfully use it.

We call this difference the Contactability Gap.

It exists whenever a business assumes it can reach a customer because a contact detail exists in its system, without knowing enough about whether that information is still useful.

OTP journeys expose that gap particularly clearly.

The customer is waiting. The communication is important. Failure becomes visible almost immediately.

Introducing number verification before the send helps close that gap by giving the business more confidence in the information being used before the communication journey begins.