Allows people to securely send you files with an encrypted upload form on your WordPress site.
Yes - however, you can try it for free for 30 days. Details can be found at http://www.javek.com/pricing.htm
This means you entered your portal url incorrectly. If your portal is located at https://www.javek.com/my-portal, you would enter "my-portal" (without the quotes) in the url box of the widget form, or the "name" attribute of the shortcode [javek-uploader name="my-portal"].
You need to enable your upload form. Login to your Javek subscription, go to the Administration tab and click "Buckets" in the right-side menu. Click the "Public Buckets/Uploads" button, check the box in the popup that says "Enable public buckets" and click "Save and Get Code". (You don't need the code - this plugin embeds the code for you)