Need help with dnsmasq dhcpscript

I'm running openwrt on a JCG Q20 router and I tried to create a script in /etc/hotplug.d/dhcp that notifies whenever a device joins my network.

Instead of the script being executed, I get this message from logread instead:

dnsmasq-script[1]: /usr/lib/dnsmasq/dhcp-script.sh: .: line 3: 3: No file descriptors available

line 3 of /usr/lib/dnsmasq/dhcp-script.sh is:

[ -f "$USER_DHCPSCRIPT" ] && . "$USER_DHCPSCRIPT" "$@"

I can get the hotplug script to run manually using ubus.

Has someone tried doing something similar and did you run into the same problem?