Currency Field Validation

Hello,

I have a Nintex form set up with a currency field from a SharePoint list.  If a user types a dollar sign into the field the form will submit but lose the data in the currency field.  We did add a label for people to NOT type in a dollar sign and 90% of users follow those instructions.  But I was wondering if there was a way to have validation added to that field to prevent the form from submitting if the field contains a $.

Using Nintex Forms and Workflows for SharePoint Online/O365