max_size fails

PHP Code:

I have this input:

    <input id="delega" type="file" class="form-control" accept="application/pdf">

I send the pdf using an AJAX request:

var data = JSON.stringify($('input[name="post_data"]').val());

    var url = `<?= base_url('appointments/ajax_register_appointment') ?>`;
    var $layer = $('<div/>');

    let formData = new FormData();
    formData.append('post_data', data);

    if (GlobalVariables.manageMode) {
        formData.append('exclude_appointment_id', GlobalVariables.appointmentData.id);
    }

    let delega = document.getElementById('delega').files[0];
    if (delega !== undefined) {
        formData.append('delega', delega);
    }

    $.ajax({
            url: url,
            method: 'post',
            data: formData,
            dataType: 'json',
            contentType: false,
            processData: false,

But if I upload a file of 172kb I get the error that is too large:

        $delega = $this->request->getFile('delega');

        // controlla correttezza file
        if (!empty($delega)) {

            
            $validationRules = [
                'delega'        => 'mime_in[delega,application/pdf]|max_size[1024]'
            ];

            if (!$this->validate($validationRules)) {
                return $this->fail($this->validator->getErrors());
            }
        }

how is that possible?