401 Unauthorized while using “auth0.com/oauth/token”


I try to use auth0 for my react-native (expo) app.
After read the documentation, i find using the “Authorization Code Flow with PKCE” is most suitable.

So first, i create an Application “Machine to Machine” and setup the callback URL.
I also created an API an add my application to “Machine to Machine Applications”

  • create an Application “Machine to Machine”
  • setup the callback URL
  • set “Token Endpoint Authentication Method” to "Post’
  • created an API an add my application to “Machine to Machine Applications”

You can see the code for the first call :

        let authUrl = `${auth0Domain}/authorize?` + this.toQueryString({
            client_id: uth0ClientId,
            response_type: 'code',
            scope: 'openid profile email',
            redirect_uri: redirectUrl,
            code_challenge: challenge,
            code_challenge_method: 'S256',

        const result = await AuthSession.startAsync({
            authUrl: authUrl

The first call is working properly, i get the Authorization code.

My problem is for getting the token :

        var dataToken = new URLSearchParams();
        dataToken.append('client_id', getEnvVars().auth0ClientId);
        dataToken.append('grant_type', 'authorization_code');
        dataToken.append('redirect_uri', redirectUrl);
        dataToken.append('code_verifier', verifier);
        dataToken.append('code', codeResult);

        var options = {
            method: "POST",
            headers: {
                "Content-Type": "application/x-www-form-urlencoded",
            body: dataToken.toString()

        fetch('https://dev-fo5rwjn9.eu.auth0.com/oauth/token', options).then(result => {
            console.log(JSON.stringify(result, null, 2));
        }).catch(error => {

Here i get an “error”: “access_denied”.

Do you know why i have this problem ? do i need to register my app as “native” ?


Finnaly, it’s working !!

The application type need to be “Native” …

Sorry for the inconvenience

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