You probably already found a solution, but this is what worked for me:
- add a submit button to the form
- add
autoProcessQueue: false
to dropzone options override the submit button's click event, and check your conditions before telling dropzone to process the queue:
$('#submit_button').click(function(e) { e.preventDefault(); e.stopPropagation(); if ( //check your conditions here ) { myDropzone.processQueue(); } else { //show error } });