Help with 403 Forbidden Error When Setting Up a Tunnel Server

[HarryPan]

I've recently been trying to set up a tunnel server, but when I run the server following the official guide, I keep getting the following errors in the terminal:

[7/3/2026 1:30:48PM UTC] Tunnel Heartbeat: The remote server returned an error: (403) Forbidden.
[7/3/2026 1:30:49PM UTC] Tunnel V2 Heartbeat: The remote server returned an error: (403) Forbidden.

I have already tried switching to a different cloud server, but the result is exactly the same. I couldn't find any similar cases online, and other tunnel server owners I've asked haven't experienced this issue, so I'm hoping to get some help here.

My setup:
OS: CentOS 7
TCP and UDP ports opened: 8054, 3478, 50000, 50001
Commands I've tried running:
nohup ./cncnet-server --name "[CN]harrypan.cn" --maxclients 32 --port 50001 --portv2 50000 >cncnet-server.log 2>&1 &
and
./cncnet-server --name "My cool server" --maxclients 200 --port 50001 --portv2 50000

Both result in the same 403 Forbidden,and they repeat it every once in a while。 No other error messages appear after that.
Does anyone know what could be causing the master server to return 403? Is there any additional configuration or whitelisting step I might have missed? Any advice would be greatly appreciated.

Thanks in advance!