UX/UI: Send input with enter and with OR without click?

I'm creating a simple chatbot where you can send an input value as message. I'm thinking about doing Enter only. A submit button would be bad for my UI but it might be good for UX. So what do you think? Do I need a submit button or do (nearly) all people know to press enter to send the message? Or should I write it somewhere that they have to press enter?

EDIT: Thanks. Will do both. :)