In case the recipient does not use “Hangout” the MMS setting for group chats needs to be deactivated. This can be done as follows:
- Group messages Google Hangouts – contextual menu / „people & options“
- Go to settings in the „people & options“ menu
- Choose SMS in settings
- Select „advanced“ and deactivate „Send MMS to group“
Now all invites will be send to a group via SMS and can also be opened and read by non-Google-Hangout users.