Rising Stars are recognized for providing high-quality answers to other users. Rising Stars receive a certificate of achievement and are on the path to becoming Community Leaders.
These messages are exactly what they say they are.
You are inviting accounts that are identified with email addresses. The accounts you are inviting in do not have any access to your Cloud system.
You will need to add these accounts to your system via invite or physically adding them to the system or permissions you want them to have.
As an example, imagine you have tried to share something with me, using the account I am using here in Community. I have an Atlassian account, tied to the email address you send the share to. I've just tried the url in the messages you are getting, and I get exactly the same message - I (rightly) do not have any access because your admins have not let me in.