If you start typing a message and leave the chat before sending it, InterChat keeps it as a draft so you don't lose your train of thought.
Drafts are saved only on your phone — they're never sent to InterChat's servers, so they don't appear if you sign in on another device. Deleting the app will remove any drafts you haven't sent.
When you come back to a chat with an unsent draft, you'll find your text still waiting in the message box, ready to finish and send.