The key is to set the text in HTML and not send it as a string.
Suppose that the text that you want to use is in a string textToShare; Please note that you will send in the HTML string, so you need to replace all of the new characters in the string <br/>
instead
theRequest.Data.SetText(textToShare);
using
theRequest.Data.SetHtmlFormat(HtmlFormatHelper.CreateHtmlFormat(textToShare));
source share