In the Venice mobile app, you can change how the Enter key behaves so it adds a line break instead of sending your message.
Open the settings menu from the prompt bar, go to the app settings, and turn off Enter Submits Chat. After that, pressing Enter adds a new line instead of sending.
On the web app, the same setting is available under Settings, in the General section (open Settings by toggling the sidebar, clicking your profile in the bottom left, then Settings). With Enter Submits Chat enabled, you can also use Shift+Enter for a line break.