Not Receiving OTP Codes? Here Are the Causes and the Fastest Ways to Fix It

OTP (One-Time Password) is an essential security layer used for login verification, account registration, password recovery, online payments, and hundreds of digital services. However, many users experience the frustrating issue of not receiving OTP SMS, making it impossible to access or verify their accounts.

In this guide, we’ll break down why OTP messages fail to arrive, what causes the issue, and the fastest ways to fix OTP SMS delivery problems—whether you're using a physical SIM, virtual number, or rented OTP service.

1. Common Reasons Why OTP Codes Don’t Arrive

There are several potential causes. Some come from your carrier, some from your device, and others from the platform sending the OTP.

1.1. SMS from service providers is blocked

The most common reason is that the phone number has blocked promotional or service SMS without realizing it.

Typical causes include:

  • You previously rejected promotional SMS (STOP/TC message)

  • Your carrier has automatically blocked repeated OTP messages

  • Your phone installed an app that filters unknown senders

Symptoms:
You receive no OTP at all from multiple platforms.

How to fix:

  • Viettel: Send MO to 199

  • Mobifone: Send KT to 999

  • Vinaphone: Send DSQC to 456

  • Disable SMS blocking / spam filtering apps (Truecaller, Messages Filter, etc.)

1.2. SIM card issues (blocked, expired, or no signal)

If your SIM is old, inactive, or rarely used, the carrier may restrict SMS services.

Fixes:

  • Check if you can call or send/receive normal SMS

  • Toggle Airplane Mode

  • Insert SIM into another phone

  • Contact carrier to reactivate

1.3. Your phone number has reached platform limits

Major platforms limit how many OTP registrations one number can perform.

Examples:

  • Facebook limits account creation per number

  • Google restricts Gmail sign-ups

  • Zalo blocks repeated registrations

  • Shopee restricts multiple seller accounts

Fix:
Use another phone number
Or use a virtual number / rented OTP service if you need multiple accounts.

1.4. OTP delivery delay due to system overload

Sometimes, the platform you’re trying to log into is experiencing:

  • High traffic

  • Server delay

  • SMS sending queue overload

Fix:

  • Wait 1–5 minutes

  • Request OTP again

  • Choose “Call me” option (if supported)

1.5. Device storage or SMS inbox is full

Older Android devices may stop receiving messages when the inbox is full.

Fix:

  • Delete old messages

  • Restart the device

1.6. eSIM issues with international OTP

Some eSIM carriers block international SMS temporarily.

Fix:

  • Switch to a physical SIM

  • Or use a virtual number that supports OTP

1.7. OTP blocked due to suspicious activity

If the platform detects unusual behavior, it may block OTP sending entirely:

  • Using VPN

  • Using proxies

  • Logging in too many times

  • Auto tools

  • Browser fingerprint mismatch

Fix:

  • Disable VPN

  • Switch to mobile data

  • Try a different device or browser

2. Not receiving OTP from international services

Some platforms do not send OTP outside the country, especially:

  • Banking & finance apps

  • Local apps (Zalo, MoMo, ShopeeVN, etc.)

  • Services with regional restrictions

Fix:
Use a local phone number for that service
Or use a global virtual number compatible with the platform.

3. Not receiving OTP when using virtual numbers or OTP rental services

If you're using an online OTP service and the code doesn’t arrive, the reason is usually one of the following:

3.1. The number you selected is not supported by the platform

Every app prefers certain countries/carriers:

  • Facebook: Vietnam, India

  • Telegram: Russia, Uzbekistan

  • Gmail: US/UK numbers

  • TikTok: US, Vietnam, Indonesia

Using a mismatched number → OTP may not arrive.

Fix:
Choose a number with high success rate for that specific platform.

3.2. OTP service is slow or overloaded

Cheap/low-quality OTP services may:

  • Delay SMS

  • Lose OTP

  • Have blocked carriers

  • Use recycled numbers

Fix:
Use a reputable provider such as a stable OTP rental platform with reliable carriers and a 1–5 second delivery time.

3.3. Wrong region selected

Common mistakes include:

  • Trying to register TikTok US with a Vietnam number

  • Creating Gmail Vietnam with an Indonesian number

→ The OTP simply won’t arrive because the region doesn’t match.

4. Quick Diagnostics to Identify Where the Problem Is

A simple rule to quickly determine the root cause:

Situation Root Cause
No OTP from ANY app SIM / carrier issue
No OTP from ONE specific app Platform issue
Number used too often Platform has blocked OTP to your number
OTP delayed Network congestion / system overload
OTP not arriving to virtual number Wrong region or carrier

5. When should you use a virtual number instead of a real SIM?

Virtual phone numbers / OTP rental services are ideal when:

  • You need many OTP codes per day

  • You work in marketing, automation, or MMO

  • You want to protect your personal phone number

  • Your SIM is restricted or blocked

  • You must receive OTP from international platforms

Benefits of using virtual numbers:

  • Receive OTP in 1–5 seconds

  • No SIM required

  • No carrier restrictions

  • Works 24/7

  • Supports multiple countries

  • Affordable (cheaper than buying SIMs)

Conclusion

Not receiving OTP codes is a common issue caused by carriers, device settings, platform restrictions, or OTP system overload. Fortunately, most issues can be fixed easily:

  • Unblock service messages

  • Check SIM status

  • Disable VPN

  • Choose the right region

  • Use a reliable virtual OTP number when needed

If you frequently need to verify accounts, test apps, or register multiple profiles, switching to a fast, stable 24/7 OTP SMS service is the most efficient solution.