A poor signal might have prevented the message from going through, causing the app to save it as a draft so you don't lose the text.
While I cannot see the content of that specific file, search results for this type of query often point to discussions about on Android or iOS devices. If your image is a screenshot of a text conversation with a red "Draft" label, Why Your Message is a "Draft"
Some users report that third-party chargers or software bugs can cause the phone to "ghost type" or save empty messages as drafts. How to Manage Draft Messages
You likely typed a message but didn't hit send before exiting the app or switching to another conversation.