Transmission port forwarding

Hi,

I am very new in this "world" with OMV5 and I just wanted to set up transmission (without vpn). I created the transmission stack (version 2,1), and it's running, but the torrents doesn't start downloading (or connecting to peers). I checked and the port is closed. I port forwarded the port what transmission gave me, but it still says it's closed. What should I try?

I have an Cisco EPC3925 EuroDocsis 3.0 2-PORT Voice Gateway. I enabled UPnP and DMZ hosting is off.

(I only have duplicati, transmission and rpi-monitor, and yes the IP is static)

I tried yougetsignal.com and the port is opened for my laptop (I don't know why), but for the raspberry it's closed.