I got what mistake I was doing. After generating the tag I had to put the code generated in the respective section.
This is an example of code generated.
I should put this in the form.
It reads something like this.
Copy this code and paste it into the form left.
And below this is another code.
And, put this code into the File Attachments field below.
This is supposed to go to the Attachments field in the mail section.
I was literally writing [your-file][your-another-file] which was wrong.
However I am still unable to figure out multiple file upload. I need to generate different file upload tags for each file to be uploaded. But being not sure how many files my client needs to upload, If my client wants to upload 3 files and I have one or only two file upload section.
It would be easier if anyone can help with multiple file upload by generating tag only once. After client uploads one file, it should give option upload more files.
Any help is appreciated.