Hi Mark,
Greetings from Syncfusion Support.
We have validated your query “Is there something about the specialnumber input that the validator doesn't like / requires?” at our end and we have to let you know that if we want to add the validation for our additional fields, it needs to be added the validation rule for the additional fields. For more reference, please visit the below UG documentation.
Also, we have prepared the sample with the same scenario. In that sample, we have used the popupOpen event to add the validation rule for additional fields.
onPopupOpen(args) {
if (args.type === 'Editor') {
let statusElement = args.element.querySelector('#specialnumber');
statusElement.setAttribute('name', 'SpecialNumber');
let formElement = args.element.querySelector('.e-schedule-form');
let validator = formElement.ej2_instances[0];
validator.addRules('SpecialNumber', { required: true });
}
}
Kindly try the above sample and get back to us if you need any further assistance.
Regards,
Vengatesh