How to identify connection issue

[http600]

Setup Server

apt update
apt install -y git
mkdir -p workspace
pushd workspace
git clone https://github.com/shadowsocks/go-shadowsocks2.git
git clone https://github.com/shadowsocks/v2ray-plugin
apt install -y golang
go install golang.org/dl/go1.16.15@latest
~/go/bin/go1.16.15 download
pushd v2ray-plugin
~/go/bin/go1.16.15 build
popd
pushd go-shadowsocks2
~/go/bin/go1.16.15 build
popd
popd

Then start

workspace/go-shadowsocks2/go-shadowsocks2 -s 'ss://AEAD_CHACHA20_POLY1305:shadowsocks1234@:1234' -plugin workspace/v2ray-plugin/v2ray-plugin -plugin-opts 'server' -verbose
2022/04/27 18:45:23 plugin.go:16: starting plugin (workspace/v2ray-plugin/v2ray-plugin) with option (server)....
2022/04/27 18:45:23 plugin.go:31: plugin (workspace/v2ray-plugin/v2ray-plugin) will listen on 0.0.0.0:1234
2022/04/27 18:45:23 udp.go:134: listening UDP on :1234
2022/04/27 18:45:23 tcp.go:103: listening TCP on 127.0.0.1:46503
2022/04/27 18:45:23 log.go:23: [workspace/v2ray-plugin/v2ray-plugin]: 2022/04/27 18:45:23 V2Ray 4.38.3 (V2Fly, a community-driven edition of V2Ray.) Custom (go1.16.15 linux/amd64)
2022/04/27 18:45:23 A unified platform for anti-censorship.

2022/04/27 18:45:23 log.go:23: [workspace/v2ray-plugin/v2ray-plugin]: 2022/04/27 18:45:23 [Warning] V2Ray 4.38.3 started

Client

build the same as server

~/Downloads/workspace/go-shadowsocks2/go-shadowsocks2 -c 'ss://AEAD_CHACHA20_POLY1305:shadowsocks1234@1.2.3.4:1234' -plugin ~/Downloads/workspace/v2ray-plugin/v2ray-plugin -socks :1026 -verbose 
2022/04/28 02:47:42 plugin.go:16: starting plugin (/Downloads/workspace/v2ray-plugin/v2ray-plugin) with option ()....
2022/04/28 02:47:42 plugin.go:33: plugin (/Downloads/workspace/v2ray-plugin/v2ray-plugin) will listen on 127.0.0.1:64803
2022/04/28 02:47:42 tcp.go:18: SOCKS proxy :1026 <-> 127.0.0.1:64803
2022/04/28 02:47:42 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:47:42 V2Ray 4.38.3 (V2Fly, a community-driven edition of V2Ray.) Custom (go1.16.15 darwin/amd64)
2022/04/28 02:47:42 A unified platform for anti-censorship.

2022/04/28 02:47:42 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:47:42 [Warning] V2Ray 4.38.3 started

2022/04/28 02:48:03 tcp.go:87: proxy 127.0.0.1:64906 <-> 127.0.0.1:64803 <-> www.google.com:443
2022/04/28 02:48:03 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:48:03 127.0.0.1:64907 accepted tcp:127.0.0.1:0

2022/04/28 02:48:07 tcp.go:87: proxy 127.0.0.1:64927 <-> 127.0.0.1:64803 <-> www.google.com:443
2022/04/28 02:48:07 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:48:07 127.0.0.1:64928 accepted tcp:127.0.0.1:0

2022/04/28 02:48:34 tcp.go:87: proxy 127.0.0.1:65054 <-> 127.0.0.1:64803 <-> www.google.com:443
2022/04/28 02:48:34 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:48:34 127.0.0.1:65055 accepted tcp:127.0.0.1:0

2022/04/28 02:48:42 tcp.go:87: proxy 127.0.0.1:65096 <-> 127.0.0.1:64803 <-> www.google.com:443
2022/04/28 02:48:42 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:48:42 127.0.0.1:65097 accepted tcp:127.0.0.1:0

2022/04/28 02:49:34 tcp.go:87: proxy 127.0.0.1:65340 <-> 127.0.0.1:64803 <-> www.google.com:443
2022/04/28 02:49:34 log.go:23: [/Downloads/workspace/v2ray-plugin/v2ray-plugin]: 2022/04/28 02:49:34 127.0.0.1:65341 accepted tcp:127.0.0.1:0

It OK it is not working, but how to identify where is the problem?

run tcpdump on :1234 at server side, there are only incoming packets, did not see any outgoing/replying packets