Can’t save forms

I took over support for a site that uses this plugin and it is currently on version 1.6.1. When I attempt to update a form, or create a new one, when I click the Save button at the top of the page I get the spinning wheel, but no updated notification.

When on a form editing screen there is this error in the javascript console:

TypeError: a.inputmask is undefined fields.min.js:4:24207

Tough place to be in not being able to edit or create any new forms. Are you able to help with this?