Credits are the cost per SMS sent to Clients via ToolDesk.
SMS allows up to 160 characters per message, or 70 characters when there is an emoji.
Each set of 160 characters is equal to 1 segment.
0 - 160 characters (a.k.a 1 segment) = 1 credit
161 - 320 character (a.ka 2 segments) = 2 credits
321 - 480 characters (a.k.a 3 segments) = 3 credits
You can use this calculator to see exactly how long your SMS is.