Custom Contact Form

I just started using the “custom contact form” plug in. I’m trying to edit a field. I’ve edited, check the field and selected “save” on the drop down field next to apply, but when I click apply the screen goes blank and displays a -1 on the upper left hand of the screen. The url shown is https://mydomain.com/wp-admin/admin-ajax.php. I’ve tried doing this to edit the field and also to delete the field and I still get the same results. Anyone know how I can either edit of delete fields?

Thank you.