Host A

root@hosta # wg genkey > privateA
root@hosta # wg pubkey < privateA > publicA

Host B

root@hostb # wg genkey > privateB
root@hostb # wg pubkey < privateB > publicB

Link-Network: 172.24.0.0/30
HostA: 172.24.0.1/30
HostB: 172.24.0.2/30

Assumption Host A is visible to Host B

Host A

root@hosta # cat /etc/wireguard/wg0.conf
# HostA - HostB
[Interface]
Address = 172.24.0.1/30
PrivateKey = <contents of privateA>
ListenPort = 51820

[Peer]
PublicKey = <contents of publicB>
AllowedIPs = 172.24.0.2/32

Host B

root@hostb # cat /etc/wireguard/wg0.conf
# HostB - HostA
[Interface]
Address = 172.24.0.2/30
PrivateKey = <contents of privateB>
ListenPort = 51820
#If something needs to happen after tunnel is up or before tunnel goes down
#PostUp = /usr/local/sbin/wg0-PostUp.sh
#PreDown = /usr/local/sbin/wg0-PreDown.sh

[Peer]
PublicKey = <contents of publicA>
Endpoint = <visible ip of HostA>
AllowedIPs = 172.24.0.1/32
# Uncomment if HostB is behind NAT Router
# PersistentKeepAlive = 25

Issue on both hosts

root@hosta # wg-quick up wg0
root@hostb # wg-quick up wg0

Host A

root@hosta # wg
interface: wg0
  public key: PUBLIC-KEY-A
  private key: (hidden)
  listening port: 51820

peer: PUBLIC-KEY-B
  endpoint: 185.69.244.140:25920
  allowed ips: 172.24.0.2/32
  latest handshake: 1 minute, 44 seconds ago
  transfer: 2.80 MiB received, 1.09 MiB sent

Host B

root@hostb # wg
interface: wg0
  public key: PUBLIC-KEY-B
  private key: (hidden)
  listening port: 51820

peer: PUBLIC-KEY-A
  endpoint: 144.76.72.57:51820
  allowed ips: 172.24.0.1/32
  latest handshake: 21 seconds ago
  transfer: 1006.68 KiB received, 2.57 MiB sent
  persistent keepalive: every 25 seconds

root@hostb # cat << EOF > /etc/systemd/system/wg0-shutdown-fallback.service
[Unit]
Description=WireGuard wg0 shutdown fallback
DefaultDependencies=no

Before=shutdown.target reboot.target halt.target
Before=wg-quick@wg0.service

Conflicts=shutdown.target reboot.target halt.target

After=local-fs.target

[Service]
Type=oneshot
RemainAfterExit=yes

ExecStart=/bin/true
ExecStop=/usr/local/sbin/wg0-PreDown.sh

TimeoutStopSec=30

[Install]
WantedBy=multi-user.target
EOF
root@hostb # systemctl daemon-reload
root@hostb # systemctl enable wg0-shutdown-fallback.service
root@hostb # systemctl start wg0-shutdown-fallback.service