You can send up to 1000 characters (7 SMS) concatenated on a single message.
If the text of the SMS is longer than the allowed characters, the SMS will not be sent and you will be alerted with an email.
Please see below for a breakdown of the character allowance and corresponding SMS credits:
|0-160 characters||= 01 SMS|
|161-306 characters||= 02 SMS|
|307-459 characters||= 03 SMS|
|460-612 characters||= 04 SMS|
|613-765 characters||= 05 SMS|
|66-918 characters||= 06 SMS|
|919-1000 characters||= 07 SMS|