cannot extract the value of "{formkey}" from response

[skione13]

I am trying to extract the value from a hidden form field for CSRF, I have tested my regex and it works but I keep getting an error in Zabbix saying the value cannot be extracted. Here is the html <input name="form_key" type="hidden" value="mtiM3tYvzyOEgEzk" />
and here is the line I've configured in zabbix: regex:name="form_key" content="[0-9a-zA-Z]{16}"

[tim.mooney]

Does the following work?

regex:name="form_key.*" value="([0-9a-zA-Z]{16})"