Large Digital Files for Sale Download Leading to 404 Error

Hello. Am trying to set up paid digital downloads using WooCommerce ‘Force downloads’ setting.

The files are big (1.6 GB) – too big to upload via:

WooCommerce>Products>Product data>Variations>Downloadable files

…WP returns a ‘file exceeds permitted file size’.

1. I have therefore FTP’d the digital files to the correct WooCommerce folder on the server.

When uploading digital files via:

WooCommerce>Products>Product data>Variations>Downloadable files

…WooCommerce (correctly) appends random characters to the end of the file name for security. No such characters are appended when I FTP the digital files to the correct place, but this should not matter. (?)

2. From FTP client I copy URL of digital file and paste this into:

WooCommerce>Products>Product data>Variations>Downloadable files>File URL

…I know this is not the right thing to do, as WooCommerce says these URLs should already be encoded.

3. When I run a test to ‘buy’ a file from the site front end, I am taken to an Error 404 page.

If I upload a small digital file via:

WooCommerce>Products>Product data>Variations>Downloadable files

…then all works fine and the file is downloaded.

Two questions:

1. Why is the 404 error page appearing for the larger FTP’d files?
2. How can I get WooCommerce to ‘encode’ download URLs, if the digital file is not uploaded via Variations>Downloadable files ?

Thank you.