def METHOD_NAME(
    self, vpn_gateway_id: str, vpc_id: str
) -> VPCGatewayAttachment:
    vpn_gateway = self.get_vpn_gateway(vpn_gateway_id)
    detached = vpn_gateway.attachments.get(vpc_id, None)
    if not detached:
        raise InvalidVpnGatewayAttachmentError(vpn_gateway.id, vpc_id)
    detached.state = "detached"
    return detached