The Notify API client changed in version 4 to take two arguments, not
three (service ID was removed in favour of the combined API key).
This gets a bit gnarly because the API key has to be at least a certain
length so it can be substringed internally.
in the NotifyAdminAPIClient, which all api traffic goes through, return
403 for any stateful requests (post, put and delete), if the following
criteria have been met:
* a current_service is set
(this prevents checks being carried out on non-service related
updates, eg editing user details)
* the service is not active
* the current user is not a platform admin
so platform admins can still update anything.
Note: Without any specific error handling, the user will see a generic
403 page. This is fine, probably - it's a relatively niche case that
you'll be editing a service you can't get to anyway
