This topic describes the problems that you may encounter when using Alibaba Cloud Short Message Service (SMS) and the corresponding solutions.

Why messages that have been sent are not received?

You can troubleshoot the issue as follows:

  • Check whether your mobile phone remains on for a long time. Turn off and restart the phone.
  • Check whether the inbox of your mobile phone is full. Delete several messages and try again.
  • If you use a dual-SIM dual-standby mobile phone, change the slot of the SIM card.
  • Check whether security software is installed on your mobile phone. The security software may block messages.

If the issue persists, put the SIM card on other mobile phones to check whether the SIM card works properly.

Types of SMS sent to Vietnam

SMS sent to Vietnam will be converted to Text to Speech Call to ensure delivery for OTP.

What are message sending rules of the US and France?

The US and France have the following message sending rules:

  • The US does not support promotional messages.
  • France does not support promotional messages.
  • SMS sending API-APIs cannot be sent to mainland China. If you want to send API messages to mainland China and use a global package, you must use both the SMS sending API and SMS sending API messages in mainland China.
  • A2P SMS regulations in India.

How many characters can I include in a single message?

Each message can be up to 1500 characters in length.

How can I set a message sending frequency?

When you set a message sending frequency, note the following issues:

  • To ensure excellent user experience, the number of messages that can be sent to one phone number within one day cannot exceed the predefined limit. The limit defined by the system is 20 messages per day.
  • You can customize a limit. However, the limit that you set cannot exceed 20.
  • A day refers to the last 24 hours from the current time. For example, if you are sending a message at 2017-08-24 11:00, the system checks whether the number of messages sent from 2017-08-23 11:00 to 2017-08-24 11:00 reaches the specified limit. If the limit is reached, you cannot send more messages.

Why does ".0" appear following the sent verification codes?

This error may occur if the data type of a JSON object is not string.

Can I send an SMS message to multiple mobile phones at a time?

No. You can submit only one mobile number when sending an SMS message.

How can I prevent SMS message flooding?

SMS message flooding occurs when malicious programs are used to send unlimited unexpected messages to mobile phones. SMS message flooding is a harassment technique that can negatively affect your business. We recommend that you use the following methods to prevent SMS message flooding:

  • Implement a CAPTCHA. You can implement a CAPTCHA on your verification code page to prevent malicious programs from calling SMS to send unsolicited messages. Before a user send a verification code, the user must enter the CAPTCHA text to confirm that the sending operation is performed by a human user. Then, the SMS server sends the verification code to the intended recipient. This technique can efficiently prevent SMS flooding attacks.
  • Set a validity period for verification codes. In most cases, the validity period is set to 60 seconds. If a verification code expires, you must retrieve another one.
  • Set a time limit for entering a verification code. In most cases, the time limit is set to 30 seconds. If you do not enter the verification code within 30 seconds, the verification code expires and you must retrieve another one.

What are possible causes for SMS sending failures?

SMS sending failures may occur due to the following causes:

  • Portability Failure: In most cases, SMS messages can be received by mobile numbers whose carriers are being changed. However, if the new carriers do not update the network routing information for the mobile numbers in time, or if the mobile numbers are transferred to the new networks within 24 hours, SMS messages may fail to be received.
  • Handset Cannot Receive SMS: Mobile phones cannot receive SMS messages in the following scenarios: 1. The memory of the mobile phones is full. 2. The mobile phones are in the flight mode. 3. The mobile phones are out of service.
  • Sending the Wrong Content: The message content is invalid. For example, mobile phones do not support the languages in which the messages are written.
  • Roaming: SMS sending failures may occur during international roaming. Whether mobile phones can receive SMS messages depends on the international roaming interconnection agreement between carriers.
  • Carrier Spam Filters: SMS messages are filtered by carriers because the messages include forbidden information.

How do I check whether a mobile number is available?

You can the following method to check whether a mobile number is available:

  • You can check the mobile number based on the international dialing rules. However, whether the mobile number exists, whether it is disabled, and whether its mobile network carrier is being changed cannot be determined.
  • If the specified mobile number meets the rules, SMS messages are sent. In this case, carriers charge you even if the mobile number does not exist and messages fail to be received.
  • Alibaba Cloud SMS can retrieve detailed information by updating the carrier route databases. In most cases, you are charged for this service.