code: def upload_invoice_signature(self, invoice_id, signature_dict):
          
          return self._create_put_request(
              resource=INVOICES,
              billomat_id=invoice_id,
              send_data=signature_dict,
              command=UPLOAD_SIGNATURE
          )
docs: Uploads a signature for the invoice
  
          :param signature_dict: the signature
          :type signature_dict: dict
          :param invoice_id: the invoice id
          :return Response