I was having difficulty getting Dropbox to work on Linux (Ubuntux 18.04), and had removed and reinstalled the dropbox client without success. Even when I reinstalled the daemon with dropbox start -i, I still never was able to get the message:
I had unlinked the Linux box via the web interface, and I had expected that completely deleting my Dropbox installation, folder, .dropbox and .dropbox-dist dirs would remove any linking info locally on my computer, hence prompting dropbox newly to set up linking to this machine when I started the daemon. However, that didn't happen. That was when I was logged in via a standard graphical desktop, which was a detail that I didn't think was relevant.
However, when I logged in remotely to the Linux box via a purely text-based ssh-window, and ran dropbox start from there, suddenly I did get the long sought after "To link this computer" message, along with the link, and that link worked.
It seems that somehow the dropbox client is better at asking for machine-linking via a text-only client than when it is run as part of a graphical X Windows desktop? This seems weird, but it appears to be what happened.
Anyway, I figured I'd post this, in case anyone else is having similar problems.