What is Filezilla?
FileZilla is one of the most popular and free open-source applications which is used in transferring files from local PC and remote servers. FileZilla traditionally supports the File Transfer Protocol over the Transport Layer Security. This software of FileZilla is available on different platforms and it's absolutely free.
FTPS is less firewall-friendly when compared to SFTP as it requires opening a number of ports in the operation.
Steps to Fix the “Unable to connect” issue
1) Error “Server sent passive reply with unroutable address. Using server address instead.”
This type of issue comes occasionally because the server is unable to connect in passive mode
2) Switch to Active mode in File Zilla and you are in.
Goto File Zilla >> Edit >> Settings >> Connection >> FTP >> Passive mode >> “Fall back to active”
Alternative Method
FileZilla => Edit => Settings => FTP=> Transfer Mode (Click on "Active" and then Tick "Allow fall back to ......"
Re-connect your FTP user !!!
By following these steps you can fix the issue when the Filezilla is not connecting.