If you are receiving this error, it means there is an issue with the link between your Daybreak Games account and your Steam Account--this is most likely caused by connectivity issues with Steam and should be resolved shortly.
Things to try:
If it is a network connectivity issue with Steam, it is a temporary issue and will resolve itself soon. Watch for network or maintence notifications from Steam and/or Daybreak Games on social media or the forums or try back in a little while.
Make sure you are logging into H1Z1 through the Steam library.