Captcha not showing

Hi
Thanks for the plugin. I use Cform since years.
I updated my forms and after reinstalled to cform2.
Captcha work on my staging but not on my prod.

Prod:

http://www.webdigit.be/wp-admin/admin-ajax.php?action=cforms2_reset_captcha&_wpnonce=16daf29235&ts=0&c1=4&c2=5&ac=abcdefghijkmnpqrstuvwxyz23456789&i=i&w=115&h=35&c=.000066&l=.000066&f=font4.ttf&a1=-12&a2=12&f1=17&f2=19&b=1.gif&rnd=79309

Staging:

http://staging.webdigit.be/wp-admin/admin-ajax.php?action=cforms2_reset_captcha&_wpnonce=657c6ef62a&ts=0&c1=4&c2=5&ac=abcdefghijkmnpqrstuvwxyz23456789&i=i&w=115&h=35&c=.000066&l=.000066&f=font4.ttf&a1=-12&a2=12&f1=17&f2=19&b=1.gif&rnd=400798

Really don’t understand why 🙁

Any ideas ?

Thanks.

https://wordpress.org/plugins/cforms2/