Unable to add members to Group

[C_Rick01]

Is this because I'm using the free MS365?

I have a ~5y old bought version of Outlook, but am trying to use the free internet MS365 version for a mixed Group of Mac/Google/MS people needing to access and use a Group Calendar.

Two weeks ago, I managed to set one up for a few people, but had to delete it for other reasons; last week I successfully created a new Group, with Calendar, but am unable to add any members - be they icloud/gmail or even Outlook.com users, with the message "The following person couldn't be added. Try Again. Anybody know why, and how to fix this?

PS. https://support.microsoft.com/ says there's Chat support for Outlook.com users, but there's no "?" icon top right, only a lightbulb. Is Chat only available for paid versions?

[#2]

@C_Rick01 

Finally managed to id the right Chat help; they confirmed this feature is only available if ALL members of the intended group subscribe to MS365... which unfortunately is not going to happen with such a mixed group. 

[#3]

@C_Rick01 I'm having the same issue and I don't believe the answer you were given.

The group I'm dealing with already has members that are not MS365 subscribers. These were added when the group was created and the group is working great with them. We have @hotmail.com, @outlook.com, @live.com, @msn.com, @att.net, @aol.com, @gmail.com, and others.

I'm trying add a couple more individuals to the group - one happens to be a MS365 subscriber. There is a @live.com account and other one is a @hotmail.com.

So I'll be trying to get my own support chat going on this. If it get's resolved, I'll report back.

[#4]

@DMeisner 

Great, let me know - especially if you ever manage to include an iOS user with no MS or Gmail account!