Facebook Product Feed Schedule using ShareFile FTP Link - curl error 56

I'm attempting to set up a scheduled fetch for a product feed in Facebook Business Manager. From what I can see, I can provide an FTP link to Facebook along with credentials and it should pick up the file.

The FTP provider I'm using is ShareFile, with the appropriate account given access to the folder the file is in. I confirmed I can use these credentials and connect to the FTP using FileZilla, so that portion should be solid. The setup in FileZilla is as follows:

Host: host.sharefileftp.com
Protocol: FTP
Encryption: Require implicit FTP over TLS (port 990)
User: domain\[email protected]
Password: ######

However, when I put the same credentials into Facebook Business Manager for the feed upload, I get the following error:

Fetching product feed from FTP server failed due to unknown reason (Curl error code: 56). Please help us by reporting the problem. You may be able to try again.

All I can find on this error is from the cURL error page:

CURLE_RECV_ERROR (56) Failure with receiving network data.

I saw a mention somewhere about needing to whitelist Facebook's IPs within ShareFile, but I can't for the life of me find that page.

FTP Details are set up in Facebook as follows:

URL: ftp://host.sharefileftp.com:990/Path/To/File.csv
Username: domain\[email protected]
Password: ######

I've been unsuccessful getting anywhere else with the Facebook documentation and I can't find a way to contact their support directly. If anyone has experience with this any help is appreciated!

EDIT: Trying this just with a direct cURL and getting the same results:

$ curl -u 'domain\[email protected]' "ftp://host.sharefileftp.com:990/Path/To/File.csv"
Enter host password for user 'domain\[email protected]':
curl: (56) response reading failed

So at this point it's probably just an issue with ShareFile itself, nothing to do with Facebook.

Solution

As @jared pointed out in the comments, using ftps did allow the cURL to work:

$ curl -u 'domain\[email protected]' "ftps://host.sharefileftp.com:990/Path/To/File.csv"

However, Facebook doesn't support ftps. It only supports ftp or sftp, which ShareFile doesn't support.

The normal ftp I originally tried didn't work because the ShareFile account used didn't have normal ftp allowed. Once that was turned on, Facebook was able to connect to ShareFile and grab the file successfully.