Recently Exotel started supporting Unicode SMSs. This means you can send an SMS in Unicode (non-ASCII) characters in your SMS. This primarily helps you send SMSs in regional languages like Hindi, Marathi, Telugu, Tamil, etc.
Sometimes when you type out your SMS in tools like MS-Word or other such software, you may find that they include Unicode characters even though they are not meant to be so. For example - the double quotes in MS-word are not the usual "" but are in Unicode. If you now copy-paste this text in your Exotel SMS textbox, you will get a message warning you that the text content contains Unicode and if you intend to send this message with Unicode characters. In the above example, you clearly did not intend to send the SMS with Unicode characters.
In such cases we suggest you copy your SMS text and paste it in "Notepad". This will help you identify which of those characters were in Unicode. You can then remove those and copy the rest of your SMS into the SMS textbox in Exotel.