Let's define "the same problem"

1 files are loaded into the /download directory

2 /pub is set to 777

3 if in windows Redirect is OFF

4 if in unix Redirect is ON

5 The Option Name for the download is set to Radio Button or Dropdown

6 When you add the download to the Attribute you see the green dot

7 The filename does not contain special characters or spaces and preferrably is a zip

8 you have the download in the /download direct and not in a subdirectory

What error are you receiving?

Can the attribute be added to the shopping cart?

Can you checkout?

Does it say the download is available or unavailable?

Do you have a link to start the download?