Error with firewalls api, shows `Server was unable to give you a response.`

Most firewalls declared on Terraform .hcl file does not get created when using tarraform as in this docs https://www.terraform.io/docs/providers/do/r/firewall.html

Shows error like this,

Error: Error applying plan:

5 error(s) occurred:

* module.default-firewall.digitalocean_firewall.outbound-ntp: 1 error(s) occurred:

* digitalocean_firewall.outbound-ntp: Error creating firewall: POST https://api.digitalocean.com/v2/firewalls: 500 Server was unable to give you a response.
* digitalocean_firewall.gluster_client: 1 error(s) occurred:

* digitalocean_firewall.gluster_client: Error creating firewall: POST https://api.digitalocean.com/v2/firewalls: 500 Server was unable to give you a response.
* module.default-firewall.digitalocean_firewall.outbound-dns: 1 error(s) occurred:

* digitalocean_firewall.outbound-dns: Error creating firewall: POST https://api.digitalocean.com/v2/firewalls: 500 Server was unable to give you a response.
* module.docker-swarm-firewall.digitalocean_firewall.swarm-mode-internal-fw: 1 error(s) occurred:

* digitalocean_firewall.swarm-mode-internal-fw: Error creating firewall: POST https://api.digitalocean.com/v2/firewalls: 500 Server was unable to give you a response.
* module.default-firewall.digitalocean_firewall.outbound-http: 1 error(s) occurred:

* digitalocean_firewall.outbound-http: Error creating firewall: POST https://api.digitalocean.com/v2/firewalls: 500 Server was unable to give you a response.