How to download excel (.xls) file from API in postman?

In postman - Have you tried adding the header element 'Accept' as 'application/vnd.ms-excel'

Try selecting send and download instead of send when you make the request. (the blue button)

https://www.getpostman.com/docs/responses

"For binary response types, you should select Send and download which will let you save the response to your hard disk. You can then view it using the appropriate viewer."

If the endpoint really is a direct link to the .xls file, you can try the following code to handle downloading:

public static boolean download(final File output, final String source) {
    try {
        if (!output.createNewFile()) {
            throw new RuntimeException("Could not create new file!");
        }
        URL url = new URL(source);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        // Comment in the code in the following line in case the endpoint redirects instead of it being a direct link
        // connection.setInstanceFollowRedirects(true);
        connection.setRequestProperty("AUTH-KEY-PROPERTY-NAME", "yourAuthKey");
        final ReadableByteChannel rbc = Channels.newChannel(connection.getInputStream());
        final FileOutputStream fos = new FileOutputStream(output);
        fos.getChannel().transferFrom(rbc, 0, 1 << 24);
        fos.close();
        return true;
    } catch (final Exception e) {
        e.printStackTrace();
    }
    return false;
}

All you should need to do is set the proper name for the auth token and fill it in.

Example usage:

download(new File("C:\\output.xls"), "http://www.website.com/endpoint");

You can Just save the response(pdf,doc etc..) by option on the right side of the response in postman check this image

For more Details check this

https://learning.getpostman.com/docs/postman/sending_api_requests/responses/