Email an invoice using default template

So there is no mention of how to achieve this in the API documentation.

Looking around this group it seems by posting an empty hash should
accomplish this.

However if I post:


I receive the error Required parameter missing: email

I’ve tried a different combination of email parameters with varying errors.
The only way I’ve been able to actually send an email is by supplying to,
from, subject and body.

Am I missing something here?