Hi Rick,

You should validate this via OnChange Client Script. Please refer below code:

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
   if (isLoading || newValue === '') {
      return;
   }
	if (newValue % 8 != 0) { // If the value is not multiple of the number 8; 
		alert("PASS ALERT MESSAGE HERE");
		g_form.clearValue('PASS FIELD COLUMN NAME HERE');
    
}

   //Type appropriate comment here, and begin script below
   
}

https://docs.servicenow.com/bundle/orlando-application-development/page/script/client-scripts/concep...

-Pradeep Sharma