Hello alvaroavs,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with logging into iMessage on your Mac. The steps in the related article are great for resolving this issue:
"If you can't sign in to your iMessage account or FaceTime, one of these solutions might help.
When you first set up Messages on your Mac, you're asked to sign in to your iMessage account with your Apple ID. Messages then automatically attempts to sign in every time you open it. Signing in to FaceTime is similar. If either app doesn't sign in successfully, try these solutions.
Check your internet connection
Make sure that your Mac is connected to the internet. You should be able to load web pages or receive email, for example.
Connect to the internet with your Mac
Check for a service outage
Check for any temporary service outages affecting iMessage or FaceTime.
Apple System Status
Check your Date & Time settings
Make sure that the date, time, and time zone are correct.
Set the date and time on your Mac
Make sure that your software is up to date
Software updates can improve the stability, compatibility, and security of your Mac, and might also resolve the issue.
Update macOS on your Mac
Check your Apple ID
To make sure that your Apple ID and password are correct, go to the Apple ID account page and sign in with the same Apple ID that you're using with Messages and FaceTime. If you're able to sign in, open the app and take these steps:
- Messages: Choose Messages > Settings (or Preferences), then click Sign Out. Sign in again with the same Apple ID you used on the Apple ID account page.
- FaceTime: Choose FaceTime > Settings (or Preferences), then click Sign Out. Sign in again with the same Apple ID you used on the Apple ID account page.
Reset NVRAM
In case the issue is related to any of the settings stored in NVRAM:
Reset NVRAM on your Mac
Check for third-party software
If you installed firewall, security, VPN, or other third-party networking software, make sure that the software isn't blocking any of the network ports used by iMessage and FaceTime. If necessary, disable the software and then try using your iMessage account or FaceTime again.
Check VPN (Virtual Private Network) and third-party software to help resolve network connectivity issues"
We hope this helps.
Cheers!