Have you tried the instructions Apple provides in the support documents:
Use iCloud File Sharing to share folders and documents with others
Share folders or documents
- To share a folder or document, do one of the following on your Mac:
- In the Finder
, select iCloud Drive, select a folder or document, click the Share button 
, then choose Share Folder or Share File. - Tip: If the item is on the desktop, Control-click it, choose Share from the shortcut menu, then choose Share Folder or Share File.
- In an app that supports iCloud File Sharing, open a document, click the Share button , then choose Share File.
2.Select the app you want to use to send the invitation.
You can use Mail, Messages, Copy Link and AirDrop to send an invitation.
3.Click the “Who can access” pop-up menu, then do one of the following:
- Choose “People you invite” to allow only invitees to access the folder or document.
- Choose “Anyone with the link” to allow anyone who receives the link to access the folder or document. For example, your invitees can share the link and give access to others not included in the original invitation.
4.Click the Permission pop-up menu, then do one of the following:
- Choose “Can make changes” to allow others to revise the items in the folder.
- Choose “View only” to allow read-only access.
5.To allow anyone to invite others to share the file, select the “Anyone can add more people” tickbox.
6.Click Share, then add the email addresses of the people you want to share with.
When the invitees receive your invitation, they can download the shared folder or file from iCloud to any of their devices. If you allow it, they can make changes to a document and you see the updates the next time you open the file on your Mac.
When you share a folder with only invited people, only they can access the files in the shared folder. To add more participants, you must change the settings of the shared folder; you can’t change the settings of an individual file within the folder.
Share files and folders in iCloud Drive on iCloud.com
Share files and folders
- In iCloud Drive on iCloud.com, select the file or folder you want to share, then click
. - Click Share Options, then choose who can access the file or folder, who can make changes, and if participants can add people to the file or folder.
- Choose how you want to share the link:
- Email: click Share. In the email window that appears, invite participants by adding their email addresses or phone numbers in the To field. Make any additional edits to the email, then click Send. The email option is only available when you have iCloud Mail turned on.
- Copy Link: after you select Copy Link, a text box appears. Add the email addresses or phone numbers of your participants. Click Share. A new window appears with the link for your file. Copy the link and send it.
When you share a folder, only the participants can view the files in the shared folder. To invite more people to access the files, you must change the settings of the shared folder. You cannot select an individual file or folder within the shared folder and add participants to it.
