erro subscribe

Esta dando erro no subscribe : Property subscribe does not exist on type void

 StackTrace
            .fromError(error)
            .then(stackFrames => {
                const stackAsString = stackFrames
                    .map(sf = sf.toString())
                    .join('\n')

                    console.log(message);
                    console.log(stackAsString);
                    console.log('o que será enviado para o servidor')
                    serverLogService.log({ 
                        message, 
                        url, 
                        userName: userService.getUserName(), 
                        stack: stackAsString}
                    ).subscribe(
                        () => console.log('Error logged on server'),
                        err => {
                            console.log(err);
                            console.log('Fail to send error log to server');
                        }
                    )
                });