Hello Brian,Can you please share more details about the server? Because its working fine at our end.Although preview of the attachment is disabled by default but that has no relation with submission failure. Is it working fine for anonymous user without attachment?

As mentioned above best approach is to use the numeric field. If server is 6.3 onwards then there is a property (Maximum Number of Digits) to set the maximum no. of allowed digits in numeric field that can control the limit of entered digits.

You can use submit action as rest end point. This submit action is used for POST and GET calls. So you can create your own *.jsp for expected result.