尝试将图像上传到Amazon S3但出现错误

Question

我正在尝试将图像上传到Amazon S3，但始终收到此错误：“ VM222：1 Uncaught SyntaxError：JSON中位置0的意外令牌<”。我不确定该怎么办。我遵循了网站上的所有示例代码。我的代码写在下面。

const uploadFile = (file, signedRequest, url) => {
    const xhr = new XMLHttpRequest();
    xhr.open('PUT', signedRequest);
    xhr.onreadystatechange = () => {
      if(xhr.readyState === 4){
        if(xhr.status === 200){
          document.getElementById('preview').src = url;
          document.getElementById('avatar-url').value = url;
        }
        else{
          alert('Could not upload file.');
        }
      }
    };
    xhr.send(file);
  }

  const getSignedRequest = (file) => {
    const xhr = new XMLHttpRequest();
    xhr.open('GET', `/sign-s3?file-name=${file.name}&file-type=${file.type}`);
    xhr.onreadystatechange = () => {
      if(xhr.readyState === 4){
        if(xhr.status === 200){
          const response = JSON.parse(xhr.responseText);
          uploadFile(file, response.signedRequest, response.url);
        }
        else{
          alert('Could not get signed URL.');
        }
      }
    };
    xhr.send();
  }

  const initUpload = () => {
    const files = document.getElementById('file-input').files;
    const file = files[0];
    if(file == null){
      return alert('No file selected.');
    }
    getSignedRequest(file);
  }

  return (
    <div style={{ maxWidth: "700px", margin: "2rem auto" }}>
      <div style={{ textAlign: "center", marginBottom: "2rem" }}>
        <Title level={2}> Upload Prompt</Title>
      </div>

      <Form onSubmit={onSubmit}>
        {/* DropZone */}
        {/* <FileUpload refreshFunction={updateImages} /> */}
        {/* kamran's code */}
        <input type="file" id="file-input" onChange={initUpload}/>

非常感谢您的帮助。谢谢