uploading xlsx file in html

[shine star]

I am trying to upload xlsx file throught upload button in simple html.
I have given <FORM ENCTYPE='multipart/form-data' method='POST' action='mypath' >
I am able to upload txt file and read at my server.
but when I try to upload xlsx file and try to upload, it gives me error as "bad input"
I have tried with attribute accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
I tried with giving image/pdf etc .. but it does not upload respective file ..its only taking txt..
please tell me how to upload xlsx file in html.