Cannot use iMessage on MacBook

Hi Bill_tgh,

Thanks for posting in Apple Support Communities! iMessage shouldn't log out on its own. We suggest making sure the software on your device is running the latest version as outdated software can cause things to misbehave:

1. "Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do."

-Update your iPhone or iPad

Restarting is also a great step to try. If it continues, let us know if you're getting a specific error message.

Cheers!