Steps to reproduce:

checkout docs at https://www.zabbix.com/documentation/3.0/manual/api/reference/item/object#item

see that there is no hint how to add items to templates. There is one info  that templateid is ro-variable. There should be a hint that you have to use hostid param to add items to templates. Also the description of hostid in the docs could provide something like

```

"ID of the host or template that the item belongs to."

```

Furthermode interfaceid is not required either when you add items to templates. It is only required when adding items to hosts.