Background:
Two vps on vt only provide ipv6. (because it's cheap). My zabbix server is in Tencent cloud. It doesn't have ipv6. So I can't monitor them.
How about this? Think of a way... I have another vps to apply for ipv6. Because it's free.
https://www.tunnelbroker.net This website can use ipv6 in the way of ipv4 channel. As long as you apply for registration, you can get one free of charge.

Then you should install zabbix-proxy using mysql.

No crap, just paste the command/configuration file/code.

1. Install zabbix-proxy

wget https://repo.zabbix.com/zabbix/4.0/ubuntu/pool/main/z/zabbix-release/zabbix-release_4.0-2+bionic_all.deb
dpkg -i zabbix-release_4.0-2+bionic_all.deb
apt update
apt install zabbix-proxy-mysql

2. Database Related Processing

Create a new mysql database and authorize links.

create database zabbix_proxy character set utf8 collate utf8_bin;
grant all privileges on zabbix_proxy.* to zabbix_proxy@localhost identified by 'zabbix_proxy';
flush privileges;

2.1 Import Table Structure

 zcat /usr/share/doc/zabbix-proxy-mysql/schema.sql.gz |mysql -uroot zabbix_proxy

3. Configure zabbix-proxy

Configuration file: / etc/zabbix/zabbix_proxy.conf

Server=118.xx.xx.xx
Hostname=Zabbix proxy
LogFile=/var/log/zabbix/zabbix_proxy.log
LogFileSize=0
PidFile=/var/run/zabbix/zabbix_proxy.pid
DBHost=localhost
DBName=zabbix_proxy
DBUser=zabbix_proxy
DBPassword=zabbix_proxy
SNMPTrapperFile=/var/log/snmptrap/snmptrap.log
Timeout=4
ExternalScripts=/usr/lib/zabbix/externalscripts
LogSlowQueries=3000

zabbix-server configuration

Locate to Management - > Agent Agent - > Create Agent. The main configuration options are as follows:
The agent agent agent name is the host name of your proxy configuration
Active mode of system proxy mode, representing proxy active link server. Active link proxy of passive mode server
Proxy address in active passive active mode is equivalent to whitelist, only specifying ip link passive mode needs to fill in proxyip and port correctly.

server creates actions to automatically add hosts

agent configuration linked to proxy

[root@vultr ~]# egrep -v '^#|^$' /etc/zabbix/zabbix_agentd.conf 
PidFile=/var/run/zabbix/zabbix_agentd.pid
LogFile=/var/log/zabbix/zabbix_agentd.log
LogFileSize=0
Server=2001:470:c:a11::2
 StartAgents=3
ServerActive=2001:470:c:a11::2
Hostname=vt1
HostMetadataItem=system.hostname
Include=/etc/zabbix/zabbix_agentd.d/*.conf

[root@vultr ~]# egrep -v '^#|^$' /etc/zabbix/zabbix_agentd.conf 
PidFile=/var/run/zabbix/zabbix_agentd.pid
LogFile=/var/log/zabbix/zabbix_agentd.log
LogFileSize=0
Server=2001:470:c:a11::2
 StartAgents=3
ServerActive=2001:470:c:a11::2
Hostname=vt2
HostMetadataItem=system.hostname
Include=/etc/zabbix/zabbix_agentd.d/*.conf

Automatically Added Successfully

Final relationship.

1. vt2 and vt1 actively link proxy. transmit data (or two-way)
2. proxy active link server transfers data (or two-way)
3. vt2 and vt1 can not directly connect server s and can not directly transfer data.