Effective protection against SYN FLOOD?

Question

DDoS Protection

Hello dear friends. The situation is the following. I have a server (used as a game) with the following characteristics (it uses ports such as 3306, 3724, 8085, 25 and a custom ssh port on which fail2ban is installed:

Intel Xeon E5-2630v4 6 cores.
30 GB RAM
SSD 800 GB
600 mbit/s port

And the second server that is used for the web:

Intel Xeon 4 cores
8GB RAM
SSD 200GB
200mbit/s port

The game server is constantly ddosed with SYN FLOOD
Here is information from netstat, the server got up 2-3 minutes after the attack, now it doesn’t even connect to SSH
Here are SYN packets from netstat - https://yadi.sk/d/Vm35No6WLxeoNw
And here is the configuration /etc/sysctl.conf

net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.tcp_max_orphans = 65536
net.ipv4.tcp_fin_timeout = 10
net.ipv4 .tcp_keepalive_time = 1800
net.ipv4.tcp_keepalive_intvl = 15
net.ipv4.tcp_keepalive_probes = 5
net.ipv4.tcp_max_syn_backlog = 4096
net.ipv4.tcp_synack_retries = 1
net.ipv4.tcp_mem = 50576 64768 98152
net.ipv4.tcp_rmem = 4096 16777216 87380
net.ipv4.tcp_wmem = 4096 65536 16777216
net.ipv4.tcp_orphan_retries = 0
net.ipv4.tcp_syncookies = 0
net.netfilter.nf_conntrack_max = 16777216
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_congestion_control = htcp
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.route.flush = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf .eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.ip_local_port_range = 1024 65535
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_rfc1337 = 1
net.ipv4.ip_forward = 0
net.ipv4 .icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_echo_ignore_all = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.core.somaxconn = 65535
net.core.netdev_max_backlog = 1000
net.core.rmem_default = 65536
net.core.wmem_default = 65536
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
fs .inotify.max_user_watches = 16777216

How competently to block all this with iptables? I surfed the Internet for 2 days and tried to do it, there are many commands with -p tcp and -m tcp and it gives me an error that Bad argument "tcp"
The attack has been going on for the 10th day. I'm already desperate.