rh-haproxy18-haproxy.service fails to start when OPTIONS are added

Issue

• haproxy fails to start when using OPTIONS in /etc/sysconfig/rh-haproxy18-haproxy:

OPTIONS="-d -f /etc/opt/rh/rh-haproxy18/haproxy/backends/backends.cfg"

• e.g:

# systemctl status rh-haproxy18-haproxy.service
● rh-haproxy18-haproxy.service - HAProxy Load Balancer
   Loaded: loaded (/usr/lib/systemd/system/rh-haproxy18-haproxy.service; disabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Wed 2020-04-29 19:12:36 EDT; 25s ago
  Process: 31862 ExecStart=/opt/rh/rh-haproxy18/root/usr/sbin/haproxy -Ws -f $CONFIG -p $PIDFILE $OPTIONS (code=exited, status=143)
  Process: 9315 ExecStartPre=/opt/rh/rh-haproxy18/root/usr/sbin/haproxy -f $CONFIG -c -q (code=exited, status=1/FAILURE)
 Main PID: 31862 (code=exited, status=143)

Apr 29 19:19:52 hostname systemd[1]: Starting HAProxy Load Balancer...
Apr 29 19:19:52 hostname haproxy[9382]: [ALERT] 119/191952 (9382) : Proxy 'main': unable to find required default_backend: 'TEST-API'.
Apr 29 19:19:52 hostname haproxy[9382]: [ALERT] 119/191952 (9382) : Fatal errors found in configuration.
Apr 29 19:19:52 hostname systemd[1]: rh-haproxy18-haproxy.service: control process exited, code=exited status=1
Apr 29 19:19:52 hostname systemd[1]: Failed to start HAProxy Load Balancer.
Apr 29 19:19:52 hostname systemd[1]: Unit rh-haproxy18-haproxy.service entered failed state.
Apr 29 19:19:52 hostname systemd[1]: rh-haproxy18-haproxy.service failed.