You may see in the billing report that the number of SMS invoiced is different - and higher than the number of SMS messages sent via Engage. This depends on the SMS sending channel set up on your Engage system, and there can be a technical reason for this difference.

SMS messages and Engage

An Engage system user interface will not register a send of an "SMS", but a send of a "message" that will be sent over the SMS channel, this means there is one message with one unique message ID that is stored in the Engage database.

An SMS as its name suggests (Short Message Service) allows sending of short messages to mobile phones. These messages are limited to 160 bytes per message. Note these are bytes and not characters, this is very important.

The 160 bytes per message is defined by the ITU (International Telecommunications Union), a branch of the United Nations as an International Standard.

Most modern phones allow "chaining" of messages, so if a message is longer than 160 bytes, extra messages will be sent, and the recipient's mobile phone re-assembles the individual SMS's in the correct order so you see only a single message arrive, even though technically there can be multiple messages in the background.

Engage will allow a chain of 3 SMS maximum per message sent to be sent in one campaign to a recipient, and will raise an error if a message is too big.

Engage encoding

Engage allows you to send SMS messages using several character encoding methods, most often:

• ISO-8859-x : (where x is a number from 1 to 15): This character mapping has 1 byte per character but cannot display certain accented characters. This is called 'single-byte encoding'. Engage can accept 160 single-byte characters in an SMS.
• UTF-8: This character mapping has 2 bytes per character, and allows sending messages using accented characters and specific languages such as Chinese or Japanese ideograms. This is called 'multi-byte encoding' Engage can accept 70 multi-byte characters in an SMS

Limitations

As noted above:

• One Engage message can generate 1, 2, or 3 SMS chained together, depending on the message length and character encoding used.
• One SMS message can contain 160 single-byte characters or 70 multi-byte characters.

Example 1

You want to send a simple SMS message without customization that is 150 characters long and is encoded in UTF-8: This will need 3 SMS sent per Engage message per recipient:

• You are using UTF-8 so each SMS will be limited to 70 characters long
• Engage will need to send 3 individual SMS to send the message: 70 in the first SMS, 70 in the second, and 10 in the third for a total of 150 characters.

Example 2

You have an SMS with customization, for example, a firstname and a last name, and the message will be encoded in ISO-8859-1. The raw message is 150 characters long.

• The first SMS is sent to "John Smith": This is 10 bytes. 150 + 10 = 160. This will be sent in 1 SMS
• The second SMS is sent to "Marylin Fotheringay": This is 19 bytes. 150 + 19 = 169. This will be sent in 2 SMS: 160 for the first and 9 for the second.

Conclusion

The number of SMS used to send a message in Engage will depend on your contract, message encoding, and any customizations, and this can cause the following limits to apply:

• Up to 3 SMS per Engage message can be generated
• 160 characters maximum per SMS if a single byte encoding is used
• 70 characters maximum per SMS if multi-byte encoding is used.
• When you go over this limit, Engage will need to use chain extra SMS to send your message.

Knowledge Base Reference ID: 201812201031