Error Accessing SharePoint Site Through My Apps

I recently created a SharePoint site and have added a couple of external guest users to it. The newly added users do not have Microsoft Office 365 accounts but can readily access the SharePoint site using the invitation link. The problem arises when they try accessing the SharePoint site through My Apps (https://myapplications.microsoft.com/). Once logged in using a Microsoft account and on the My Apps page they can see an Office 365 SharePoint Online icon but once clicked the guest users receive the message (see the image below). I would be thankful for any help in this matter.