When you send a message in chat, you will see that it says ‘Sent’ in green at the bottom of the message next to the time it was sent.
If your message doesn't send, an error will show that the message was unable to send. To resend the message, just hold your finger on the message, a pop-up will appear, and just tap resend.
SALT doesn't tell you if or once a message has been read. The world of dating can be quite emotional anyway and so having to also consider, or worry about, why someone hasn't responded to your message yet, even though they've read it, is not something that helps anyone on their dating journey.