Failing to exchange authorization code for tokens, status 400 (bad request)

Hello,

I've run into an error trying to exchange the authorization code returned after a user is authenticated with AWS Cognito for an access token. The error logged on the console is "Error exchanging authorization code for tokens: Error: Token request failed with status 400". I've compared the syntax to the documentation here (https://docs.aws.amazon.com/cognito/latest/developerguide/token-endpoint.html) and double-checked the other information, but I can't figure out where the issue is coming from. Why am I getting a bad request?

I've provided the code below. The exchangeCodeForTokens function contains the POST method that leads to the bad request error.

If someone could help me soon, I would greatly appreciate it!

Thanks,

Jared

    function getAuthorizationCodeFromURL() {
        const urlParams = new URLSearchParams(window.location.search);
        return urlParams.get("code");
    }

    async function exchangeCodeForTokens(authorizationCode){
        const tokenEndpoint = "https://myDomain.auth.us-west-2.amazoncognito.com/oauth2/token";
        const clientId = "myClientID";
        const clientSecret = "myClientSecret"; 
        const encodedAuthCode = btoa(clientId + ":" + clientSecret);
        const authorizationString = "Basic " + encodedAuthCode; 
        console.log(authorizationString);
        const redirectUri = "https://www.myDomain.com/menu.html"; //the configured redirect URI

        try {
            const response = await fetch(tokenEndpoint, {
            method: "POST",
            headers: {
                "Content-Type": "application/x-www-form-urlencoded",
                "Authorization": authorizationString,
            },
            body: `grant_type=authorization_code&client_id=${clientId}&code=${authorizationCode}&redirect_uri=${redirectUri}`,
            });

            if (!response.ok) {
            throw new Error(`Token request failed with status ${response.status}`);
            }

            const tokenData = await response.json();
            return tokenData;
        } catch (error) {
            console.error("Error exchanging authorization code for tokens:", error);
            throw error;
        }
    }

    function parseUserIdFromToken(idToken){
        // Decode the JWT part of the ID token using the atob function
        const jwtPayload = JSON.parse(atob(idToken.split('.')[1]));
        console.log(jwtPayLoad);
        return jwtPayload.sub;
    }

    //usage:
    const authorizationCode = getAuthorizationCodeFromURL();
    console.log(authorizationCode);
    exchangeCodeForTokens(authorizationCode)
    .then((tokenData) => {
        const accessToken = tokenData.access_token;
        const idToken = tokenData.id_token;
        // Parse user information from ID token
        const userId = parseUserIdFromIdToken(idToken);
        // Use the tokens and user information as needed
    })
    .catch((error) => {
        console.log('error', error);
    });