can't upload proof of payment

why my client can't upload proof of payment in file upload column, can u help me fix this problem?

thank you

I tried your form, and it seems to upload files without a problem:

What type of file is your client trying to upload? It may also depends on the file type, please check this guides:

http://www.jotform.com/help/29-Upload-Field-Allowed-File-Types

http://www.jotform.com/help/33-Changing-the-Upload-Size-Limit

If the issue still happens, please let us know what browser version and operating system your client is using, in order to reproduce the issue.