@ypandey ,
Is email configured for your instance/environment? Are you trying in any trail instance?
To validate invitation, go to advanced find->search for email messages entity and click results to check whether any email has been generated for invitation. Sort by desc for created on to get latest records.
If so, then functionality is working fine. Email is not configured in the instance.
If it answers your question, accept it as solution.
Regards,
Prakash
