We have a series of groups that initially are going to be used for subscribing t

Just build a small process that implements this. This is in line with Appian best practices.

Thanks, but how would this be done? Which Smart Services as the Join Group smart service page has this to say about itself. All the groups we will be using are restricted or greater

"The Join Group smart service allows you to select a public group and add yourself to it as a member, when the group has an Automatic group membership policy.
? You cannot use this smart service to join a group that has a restricted or exclusive membership policy. "

Use the smart service "Add Group Members" set assignment to designer and ensure that the designer is a system admin or at least admin of the groups.

You built a process that asks the user to which grou phe wants to join, then asks the group owner whether he wants that too. Finally add the user to the group or send him a rejection message.

Thanks. I can take it from here.

You are welcome.