Prevent Users from resharing toplevel shares but let them reshare child folders

Hi guys

I’m running Nextcloud 20.0.7 on debian server. I have a external storage attached which I like to share with customers.

The thing is that I share a department folder with the employees of that departmant. In this share we have different folders which belong to our customers. The employees should then share the cumstomer folders with their customers. This works good so fare. The problem is that the employees can reshare the department folder which is not good. I can prevent them from reshare the department share but then they’re prohibited from sharing single customers folders.

Department_Folder
Customer_01
Customer_02
Customer_03

I can’t use the app “group folders” because I can’t configure the external Storage so that’s no option.

Do you have any idea how to configure it?

Best regards
Daniel