Spark 2.6.3: Transmitter and Receiver system messages on File Transfer?

When I transmit a file to a user who is definately online (I know this because it says “online” on their main spark session window, and there is also a green dot there), I get the following system message in my own chat window:

The user is offline. Will auto-send test.txt when user comes back online.

The Receiver of the file gets the following system message in their chat session window:

You have just been sent offline files(s).

What does this all mean. Did I code something wrong. What should I do to debug this? Does the receiver have to do something to be able to see the “accept” and “reject” buttons.

Thank you,