When there is an active chat with another device, use the box at the bottom of the chat window to send messages. Underpass accepts any Unicode text characters, including emoji. Text can be typed in the box or pasted from another app.
In addition to text, Underpass allows you to send almost any kind of file or image. The data will be completely encrypted, just like all text is encrypted. If you have a file or image in another app that you want to send, switch from Underpass to the other app, copy the file or image, then switch back to Underpass and paste the file or image into the same box that you use for text.
When you have entered your message in the box and want to send it, just press the Send button. The Send button sends the message and clears the box, readying it for your next message. You and your chat partner can type and send messages simultaneously. While you are entering a message, but before you send the message, your partner will see a status line in the chat window to know that you are typing.
You can send a file of up to 4 GB in size with Underpass. When you send large files, it is important to note that Underpass sends each message sequentially in full. After you send a file, you can immediately start typing again and send another message, but the other device will not see the second message until the entire file has been received, which may take some time, depending on the speed of your network connection. The receiver will display a status line in the chat window when a file download is in progress.
Next: View and save received files