Fitbit URL callback giving a response of NULL - aws-lambda

Question

I'm having trouble getting a response from a callback uri and I would really appreciate any help you could give me.
I am trying to use the Fitbit API which requires you to use a callback url to get an Auth Code.
Workflow:
1. Go to Fitbit url to get user to allow the app access to their personal data.
2. User agrees to the conditions
3. User gets redirected to my API
4. The API returns the code from (Code is located in URL and I can access it)
5. I console.log the code out to verify it
6. API returns the code
7. I work with code then exchanging it for an access token.
The problem is that I don't return the code (Or anything )when I return to the app even though I can console.log it on the API. The response I get is NULL
Here is the URL:
url = "https://www.fitbit.com/oauth2/authorize?response_type=code&client_id=CLIENT_ID&redirect_uri=https://REDIRECT_URL&scope=activity%20heartrate%20location%20nutrition%20profile%20settings%20sleep%20social%20weight&expires_in=604800";
I then open the URL in the InAPPBrowser successfully:
if (url !== "") {
const canOpen = await Linking.canOpenURL(url)
if (canOpen) {
try {
const isAvailable = await InAppBrowser.isAvailable()
if (isAvailable) {
const result =InAppBrowser.open(url, {
// iOS Properties
dismissButtonStyle: 'done',
preferredBarTintColor: 'gray',
preferredControlTintColor: 'white',
// Android Properties
showTitle: true,
toolbarColor: '#6200EE',
secondaryToolbarColor: 'black',
enableDefaultShare: true,
}).then((result) => {
console.log("Response:",JSON.stringify(result))
Linking.getInitialURL().then(url => {
console.log("Tests: ",url)
this._setTracker(url as string);
});
})
} else Linking.openURL(url)
} catch (error) {
console.log("Error: ",error)
}
}
}
From here the URL opens successfully.
Here is the API now which is done in Typescript on AWS serverless and Lambda
export const handler: APIGatewayProxyHandler = async (event, _context, callback) =>{
let provider = event.path
//prints code
let x = event.queryStringParameters
console.log("Code: ",x)
const response = {
statusCode: 200,
body: "Success"
};
return response;
}
Please let me know if further detail is required?
Thank you!

Answer 1

Right so it turns out what I was doing was correct apart from the response should have been 301 which is a redirect response.
const response= {
statusCode: 301,
headers: {
"location": `app://CALLBACK RESPONSE ADDRESS?type=${provider}`
},
body: "Boom"
}