File Transfer via IP address

I have static public IP address. My openfire domain name is “ofs”. Ports 5222 and 7777 are opened. Messaging works without problems. File Transfer Proxy Settings reported address - my static public IP.
Server - CentOS 8, Openfire 4.4.4, without LDAP integration
Clients - Spark 2.8.3 for Windows.
Is it possible to transfer files without FQDN (witch I doesnt have) through internet?Scheme

I can’t say if this is supposed to work this way. But you can try 2.7.7, which historically works better with file transfer on different subnets https://github.com/igniterealtime/Spark/releases/tag/v2.7.7
Or if you are curious, you can try latest nightly build for 2.9.0 and enable In-Band Bystreams Only setting in Preferences > File Transfer and try that https://www.igniterealtime.org/downloads/nightly_spark.jsp