When integrating your Hubspot account with your Salesmsg account you may encounter this error message. Not to worry..here is the simple fix.
After clicking your profile icon on the bottom left corner, go to Settings. From here you will have the ability to select from a number of options in the General Settings column on the left side of the page. Click "Integrations" then the blue "Connect" tab for Hubspot.
Once you are on the Contact Access page, don't forget to check Unassigned as displayed in the diagram below!
If the issue still persists, then please ensure that you have the Marketing > Lists enabled for the user.