code: def send_invoice_email(self, invoice_id, email_dict):
          
          return self._create_post_request(
              resource=INVOICES,
              billomat_id=invoice_id,
              send_data=email_dict,
              command=EMAIL,
          )
docs: Sends an invoice by email
          If you want to send your email to more than one persons do:
          'recipients': {'to': ['bykof@me.com', 'mbykovski@seibert-media.net']}}
  
          :param invoice_id: the invoice id
          :param email_dict: the email dict
          :return dict