Solved the initial issue: I binded the external ip 188.XXX.XXX.XXX to the local one 192.168.XXX.XXX and the ftp server accepts connections. Now I stumbled into another issue. I receive the following error when logging in to ioGUI.
3:28:16 wSock_Error() -> Connection is forcefully rejected (10061)
23:28:16 ----------- connection closed -----------
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