Hi Eascards,
Here is errors:
1 On delete your button you invoke "calf" datasource that's "update" service.
2 In "detete" service mapping you have wrong link to "id" parameter. Should be from "itemId" to "id".
3 In your delete service you have wrong but should be:
{{database_url}}/collections/Calf_data/{_id}
I've fixed your APP.
Now "delete" service is work.
Regards.