Depending on the length and the characters used in your SMS Content Template, you may be charged for multiple SMS segments.
To do a quick verification, you can paste your message in this tool to get an approximation of the number of segments. Of course, if you are including a URL in the content template, the number of characters created when the SMS is generated will be used and may have to be sent in more than one segment.
https://twiliodeved.github.io/message-segment-calculator/
1) Open your SMS content template
2) In the Body menu, click on View and select Source Code
3) Take a copy of the content of the Source Code box
4) Open https://twiliodeved.github.io/message-segment-calculator/
5) In the SMS Message box, paste the content copied in step 4
You will see the number of segments, the number of characters that will be sent. Note that if you are using the @Model.TrackingUrl property, it may be longer. You can type in an example here rather than the property to view a more accurate length.
Note: This tool is provided as rough estimate only.