To get access to your messages, 2 of your friends need to register with your personal invite link after being invited. Unfortunately you don’t get access just for inviting them, they really need to use your link.
If your friends have registered and you don’t have access to your messages, they might have forgotten to use your invite link. No problem though – just send an email to firstname.lastname@example.org with your friends' names and email addresses and we’ll look into it. No friendship breakup needed.