Missing error messages

Invite Anyone Version 1.2.1
On a single wordpress site

If I enter 1 single email address into the field
“Enter email addresses below, one per line.”
and if that email address is a problem email address (e.g. used/unsafe/invalid etc) and complete the rest of the form, I receive the message:
“Please correct your errors and resubmit.”
but no further details are provided as to what the exact problem is. The error messages in this case do not appear to be being bubbled up from the code to the GUI

Looking at the code briefly it seems like $returned_data[‘error_message’] is not being appended to the $success_message before the redirect on error.

https://wordpress.org/plugins/invite-anyone/