When exchanging messages with someone, it's always wise to start of with a small message (3-4 lines long). Or if you are responding to a message with someone, try to keep your messages about the same length as theirs.
If they just say "Hi." just say "Hello" back.
This gives them feedback but allows them to keep directing the conversation.
You don't want to be the only one putting in all the effort to talk.
Otherwise you end up with this:
(Click on the pictures to enlarge them.)
Don't do this. You'll just waste your time. Like I did.
At least I can laugh about it.