In my SharePoint site I have enabled sharing with external users and it works well.
But, when I want to alert the same external user with an email ("Alert me when items change" - "send alerts to"), I am getting the message :
"Your organization's policies don't allow you to share with these users. Go to External Sharing in the Office 365 admin center to enable it." (but it IS enabled).
It is working if I use Flow, so no real problem, the thing is our customers want to use the alert function. Any ideas? Is it a bug? Grateful for answer.