post https://app.pennylane.com/api/external/v2/customer_invoices//send_by_email
This endpoint allows you to send a finalized, imported customer invoice or credit note
by email to your customer. This requires that the PDF file for that document
has been generated (this process can take a few minutes), so if you just created
the invoice in our system, we may return a 409 error. You should
retry the request in a few minutes - if you receive a 204 response, that means
that the email is on its way. For more information about email sending, please
read this guide.
This endpoint requires one of the following scopes:
customer_invoices:all