@Peter-Hogarth Are write permissions enabled on your Mac storage?

I don't use a Mac, but this is what Google says:

Select the shared folder in the Finder.

Go to File > Get Info or press Command-I.

Expand the "Sharing & Permissions" section (if it's not already).

For each user or group, choose the appropriate permission setting:

Read & Write: Allows users to open, modify, and create files. 

Read Only: Allows users to open files, but not modify them. 

Write Only (Drop Box): Allows users to only write to the folder, not open existing files. 

No Access: Prevents users from accessing the shared folder. 

Applying Permissions to Subfolders (Optional):

If you want to apply permissions to all files and subfolders within a shared folder, click the Action pop-up menu at the bottom of the Get Info window and choose "Apply to enclosed items".