连接被拒绝,但是端口是开放的

My Idea was to make netcat-Connection between two devices in different LAN; Now I looked in settings of WiFi-Router and created a port forwarding; port 4004 of router should now be able to connect me to the port 9009 on my device; on that device I started nc -l -p 9009 to open the port for listening; Now from extern I try to connect: nc <router-ip> 4004 All I get, is connection refused -_-

PS: trying on canyouseeme.org told me the port is open ¯\_(シ)_/¯