Can't get access token: InternalFailure:http://internal.amazon.com/coral/com.amazon.coral.service

I'm trying to add amazon sign in following "The Authorization CodeGrant" I get the code client side and send it to my node js express server but can't get the access token from amazon. I get 500 Internal Storage Error and:

x-amzn-errortype': 'InternalFailure:http://internal.amazon.com/coral/com.amazon.coral.service/'

My code:

async function getAmazonAccessTokenFromCode(code) {
    try {
        const { data } = await axios({
        url: 'https://api.amazon.com/auth/o2/token',
        method: 'POST',
        headers: {
        "Content-type": "application/x-www-form-urlencoded"
        },
        params: {
            grant_type: "authorization_code",
            code,
            client_id: "my_client_id",
            client_secret: "my_client_secret"
            redirect_uri: 'http://localhost:3000/amazon-auth',
        }
    })
    console.log("data", data)
    // console.log(data) // { access_token, token_type, expires_in, refresh_token }
    return data.access_token
    } catch (err) {
    console.log("err", err)
    return null
    }
}

Any help would be much appreciated!