Yii2 Pjax update div with flash message issue - ajax

Question

i've a problem with Pjax and Yii2.
I have a view with a select input.
When i select an option i load a form via Ajax into a modal window.
If i submit the form i'll make a second Ajax call to a Controller function. In the controller i set a flash message and return an array.
In my jquery code if i use Pjax to reload the div where i see the flash message the entire page is reloaded.
I use timeout false but i think the problem is because i made two ajax call and so pjax reload the entire page. How i can prevent this ?
Pjax container
<!-- START PJAX -->
{Pjax id='refresh-flash' timeout=false}
{AlertBs4::widget(['options' => ['class' => 'show']])}
{/Pjax}
<!-- END PJAX -->
view
<div class="modal" id="modal-form" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
<div class="modal-dialog" role="document" style="max-width:900px;" >
<div class="modal-content" >
<div class="modal-header">
<button type="button" class="close" data-dismiss="modal" aria-label="Close"></button>
</div>
<div class="modal-body" >
<!-- Here goes the form -->
<div class="modal-footer">
<button type="button" class="btn btn-default" id="apiCall" data-pjax="0">Ok</button><!-- this button makes the second ajax call -->
<button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
</div>
</div>
</div>
</div>
JS
$(document).ready(function(){
//Get Starter html
let html_start = $('.modal-body').html();
$('#eventi-event_trasp').on('change',function(){
let trasp = $(this).val();
$.ajax({
url: '$url',
type: 'get',
data: {
trasp_cod : trasp
},
success: function (data) {
if(data){
$('.modal-body').empty();
$('.modal-body').append(data);
$('#modal-form').modal('show');
}
},
error: function(data){
console.log(data);
}
});
});
//Click ok from form loaded via ajax
$('#apiCall').on('click',function(event){
$.ajax({
url: $('#form_corrieri').attr('action'),
type: 'post',
data: $('#form_corrieri').serialize(),
success: function (data) {
// THIS CAUSE RELOAD ENTIRE PAGE
//$.pjax.reload({container: '#refresh-flash', async: false, timeout: 0 ,push: false, replace: false});
$('#eventi-eventi_info').val(data);
$('#modal-form').modal('hide');
},
error: function(data){
console.log('error');
}
});
//$.pjax.click(event, {container: '#refresh-flash'})
});