As I following through this tutorial I installed OpenVPN on my server
https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-ubuntu-18-04

and I needed to limit bandwidth for the users so regarding to this tutorial I set a bandwidth limitation for the server

https://netbeez.net/blog/how-to-use-the-linux-traffic-control/
I just used 2 commands for set limit for bandwidth

apt-get install iproute2
tc qdisc add dev eth0 root tbf rate 1mbit burst 32kbit latency 200ms

Also I set sever.conf up with the underneath configuration

sndbuf 0
rcvbuf 0

and add these lines to the ovpn client file

sndbuf 393216
rcvbuf 393216
push "sndbuf 393216"
push "rcvbuf 393216"

but unfortunately my openVPN is unstable and it doesn’t work well, it just work for a few seconds and after the seconds it Interrupts the internet traffic.

so is there anything else for limiting the bandwidth for each user in DigitalOcean Droplets?