SDK for JavaScript v3 - "Error: TypeError: NetworkError when attempting to fetch resource"

I followed this tutorial to get started using the AWS SDK for JavaScript (version 3) within React Native apps, in order to, say, create and delete buckets stored in Amazon S3. I completed all the steps in the tutorial, but ran into an issue on Step 6: running the example React Native app. The app does run in my browser, fortunately. The problem is, the app keeps giving me the error message in the question title, whenever I type a bucket name into the text input field and subsequently press the button that calls this asynchronous JavaScript function for creating buckets:

const createBucket = async () => {
    setSuccessMsg('');
    setErrorMsg('');
  
    try {
        await client.send(new CreateBucketCommand({ Bucket: bucketName }));
        setSuccessMsg(`Bucket '${bucketName}' created.`);
    } catch (e) {
          setErrorMsg(e);
    }
};

What gives? I successfully created a Cognito Identity pool and attached the AmazonS3FullAccess policy to the unauthenticated identities IAM role. And I am positive that I provided the correct credentials—region and identity pool ID—within the React Native code.

If it matters, I used Expo, not the React Native CLI, to create and run the app.