Files are not stored on server

explained here https://contactform7.com/file-uploading-and-attachment/#How-your-uploaded-files-are-managed

Thanks for prompt reply.

I have reviewed your explanation but and I have checked the permission of parent directory and it is 755. However, wp_uploads folder is also created by default but not any single files is stored after form submission.

I have checked the log file for error but it seems like not any single error is generated.

Now, what is the issue for the same?