I tried this :
But get error: "Access denied. You do not have permission to perform this action or access this resource."
Knowing that accessing the list 'Clients' works!
I believe when you create an AppId and AppSecret for SharePoint, There is a step when you use Permission Request XML in order to give permission the your app, you should give it "FullControl" right to let you do what ever action you want.
<AppPermissionRequests AllowAppOnlyPolicy="true"> <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" Right="FullControl" /> </AppPermissionRequests>
I hope this will fix your error,
You likely have "Contribute" access to the list, which will allow you to view, add, edit and delete items in the list, but not make any changes to the list itself.
What you need is "Edit" permission, because that adds the ability to manage lists, which will allow you to change the permissions set on the list itself.