Port closed even when forwarded in router

[ThePatricide]

I've forwarded port 51413 to the IP-address of my Home Assistant server. However, Transmission still reports the port as closed in the GUI. I've used all the default config. Downloading works, but I'd like to have the port open of course for performance reasons. This is in the logs:

[2021-12-22 11:19:02.910] Port Forwarding (NAT-PMP) initnatpmp succeeded (0) (/home/buildozer/aports/community/transmission/src/transmission-3.00/libtransmission/natpmp.c:73)
[2021-12-22 11:19:02.910] Port Forwarding (NAT-PMP) sendpublicaddressrequest succeeded (2) (/home/buildozer/aports/community/transmission/src/transmission-3.00/libtransmission/natpmp.c:73)
[22/Dec/2021:11:19:04 +0100] 409 141.101.105.136, 172.30.33.8, 172.30.32.1(172.30.32.2) POST /rpc HTTP/1.1 (Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36 Edg/96.0.1054.62)
[22/Dec/2021:11:19:04 +0100] 200 141.101.105.136, 172.30.33.8, 172.30.32.1(172.30.32.2) POST /rpc HTTP/1.1 (Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36 Edg/96.0.1054.62)
[2021-12-22 11:19:04.908] Port Forwarding State changed from "Not forwarded" to "Starting" (/home/buildozer/aports/community/transmission/src/transmission-3.00/libtransmission/port-forwarding.c:106)
[22/Dec/2021:11:19:08 +0100] 200 141.101.105.136, 172.30.33.8, 172.30.32.1(172.30.32.2) POST /rpc HTTP/1.1 (Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36 Edg/96.0.1054.62)
[2021-12-22 11:19:10.909] Port Forwarding State changed from "Starting" to "???" (/home/buildozer/aports/community/transmission/src/transmission-3.00/libtransmission/port-forwarding.c:106)