I would write this as

type StationType = {
  code: String,
  label: String,
}

function StationDetail({ station } : {station : StationType}) => {
  const {
    code,
    label,
} = station;

It's necessary to declare the type of the object parameter that the function accepts.

I tried your example and got No errors!, because Flow doesn't require type annotations on private functions.

If instead I add an export like this:

// @flow
export const StationDetail = ({ station }) => {
  const {
    code,
    label,
  } = station;
  return code + label;
};

I get the following error. (Which I assume is close enough to what you are seeing.)

Error: 41443242.js:2
  2: export const StationDetail = ({ station }) => {
                                   ^^^^^^^^^^^ destructuring. Missing annotation


Found 1 error

You can solve that in at least two ways. The better way is to add a type annotation for the function argument. For example:

export const StationDetail =
  ({ station }: { station: { code: number, label: string } }) =>

or

export const StationDetail =
  ({ station }: {| station: {| code: string, label: string |} |}) =>

or even

type Code = 1 | 2 | 3 | 4 | 5 | 6;
type Radio ={|
  station: {| code: Code, label: string |},
  signalStrength: number,
  volume: number,
  isMuted: bool,
|};
export const StationDetail = ({ station }: Radio) =>
  ...

if you want to make sure the StationDetail is always called with a proper Radio object even though the current implementation only looks at the station field.

The other alternative is to change the first comment to // @flow weak and let Flow infer the argument type on it's own. That is Less Good™ because it makes it easier to accidentally change your public API and makes your actual intentions less clear.

In order the object destructuring work you should provide the appropriate object structures on the right side of the assignment. In this particular case {station} as the function argument (left side of the assignment) should be fed by something like {station:{code: "stg", label:"stg"}}. Make sure you are calling the StationDetail function with an appropriate object as argument like.

var StationDetail = ({ station }) => {
  var {code, label} = station;
  console.log(code,label);
},
    data = {station: {code: 10, label:"name"}};

StationDetail(data);