Problem: Same one mentioned below two years ago:
Dateformat in form datefield? -> Validation failed: Invalid input
Validation fails on the date field because it's looking for a specific format, yyyy-mm-dd. But this is only happening in lesser browsers that don't have the date calendar pulldown tool where a date can be clicked on. Strange though that when the calendar tool is available (in most browsers), it puts a placeholder in the field formatted as mm/dd/yyyy, allows you to type the date that way, yet delivers the date to the submitted data file and/or email as yyyy-mm-dd. And that's how I figured out what I needed to do as a workaround.
My workaround:
I put a placeholder showing the default date format the form is looking for which shows up only in those browsers that don't have the pulldown calendar. For example:
arrival:
type: date
label: 'Requested Arrival Date'
placeholder: yyyy-mm-dd
It would be nice though if I knew where the default date format is set for forms in the Grav code. Then maybe it could be changed to mm/dd/yyyy, as most people filling out my client's forms would type it.
If anyone knows, please respond.