You should try JSON

const URL = 'https://letsrevolutionizetesting.com/challenge.json';

function makeCall(url) {
    return fetch(url).then(response => response.json());
}

function startChallenge(url) {
    return makeCall(url)
        .then(response => {
            const {follow} = response;
            
            if (follow) {
                return startChallenge(follow.replace('challenge?', 'challenge.json?'));
            }
            
            return response;
        });
}

startChallenge(URL)
    .then(({message}) => console.log(`Result is: ${message}`))
    .catch(error => console.log(`Error: ${error}`));