从S3复制对象时出错 Golang "NoSuchKey:指定的键不存在"

我想把一个文件从一个文件夹复制到同一个S3桶上的另一个文件夹。在这样做的时候，我得到一个错误 NoSuchKey: The specified key does not exist ，我的代码如下。

sess, err := session.NewSession(&aws.Config{Region: aws.String("ap-south-1")})
if err != nil {
    return nil, err
Oldpath := "folder1/folder2/a+b.pdf"
newBaseFolder  := "folder3"
svc := s3.New(sess)
bucketName := "mybucket.test"
source := bucketName + "/" + oldPath                                 // Oldpath = "folder1/folder2/a+b.pdf"
                                                                     //newBaseFolder = "folder3"
newPath := newBaseFolder + "/" + strings.SplitN(oldPath, "/", 2)[1] //newPath = "folder3/folder2/a+b.pdf" 
_, err = svc.CopyObject(&s3.CopyObjectInput{
            Bucket:     aws.String(bucketName), // bucketName = "mybucket.test" 
            CopySource: aws.String(url.PathEscape(source)),
            Key:        aws.String(newPath)})
if err != nil {
        return nil, err
"err": "NoSuchKey: The specified key does not exist."
"status code": 404