It’s possible this is related to a DBL upgrade, which would make Paratext 8 incapable of communicating securely with the DBL, and thus the error message.
I’m sorry you didn’t like Paratext 9. My suggestion would be to watch at least the first 4 videos here to get oriented, and try it again. It’s been suggested to use Paratext 9 in the morning and Paratext 8 in the afternoon to help ease the transition.
What’s New in Paratext 9?
After getting used to it, I don’t like Paratext 8 anymore. It feels clunky and confusing in comparison. Paratext 9 seems much more intuitive, once you know where to start (which is why I recommend the videos).