ahhh.... so, in release notes for 9.4
Limited multiple-context support
The REST API agent can now be enabled in multi-context mode; the CLI commands can be issued only in system-context mode (same commands as single-context mode).
Pass-through CLI API commands can be used to configure any context, as follows.
https://<asa_admin_context_ip>/api/cli?context=<context_name>
If the context
parameter is not present, it is assumed that the request is directed to the admin
context.