Why Do You Charge a Credit per Message Segment?
When wireless carriers (like Verizon and ATT, for example) break up text messages into multiple segments they charge us to deliver those messages on your behalf.
We pass those costs on to you in the form of credits.
Segments are usually 160 characters for the GSM-7 format and 70 characters for the UCS-2 format. GSM-7 is the standard format, but UCS-2 is almost always used if your message contains emojis.
These formats and the estimated number of credits you will be using will be indicated before sending or scheduling any message.