What is the difference between Active and Passive for FTP?

The following gives a detailed explanation between the two:

http://www.slacksite.com/other/ftp.html

The following gives more details on potential problems causes by using one or the other:

http://www.ncftp.com/ncftpd/doc/misc/ftp_and_firewalls.html

By default SyncBackPro, SyncBackSE, SyncBackLite and SyncBackFree use passive mode. In most cases you do not need to change it. However, if when running a profile the connection times out when trying to scan the FTP server, try switching to active mode (by unticking the passive option).

SyncBack Touch

An alternative to using FTP is to use SyncBack Touch. SyncBack Touch is a cross-platform file server. It lets SyncBackPro and SyncBackSE copy files to and from another device, e.g. Windows, macOS, Linux or Android device, over the network (LAN or Internet) just like an FTP server. SyncBackFree and SyncBackLite cannot use SyncBack Touch.

Simply install SyncBack Touch on the device you want to the access the files on and then create a profile in SyncBackPro/SE to use that device.

The advantages to using SyncBack Touch instead of FTP are that you can copy open/locked files, it's far simpler to set-up, doesn't have all the compatibility problems of FTP and doesn't require complex firewall/router configuration (there is no active or passive connection issue).