If you’ve created any manual port forwarding rules, you’ll need to disable UPnP.
What’s the full diagnostic message displayed in your screenshot? It’s partially obscured - in particular, we’re looking for the full error code in the bottom line.
I recommend trying a different port assignment value in the meantime - 56000 instead of 55000, for instance.
If you’re still having issues, I’d search for the name of your internet service provider in this forum to see if any other ARC users have verified the ISP’s use of carrier-grade NAT (CG-NAT). That’s a known blockage for port forwarding above your account level.
I’ve taken a glance at ARC diagnostics associated with your account to see if this was resolved, but I wasn’t able to confirm from the information available. ARC hasn’t seen our servers in some time - are you still having issues with port forwarding?