Hello, I have a question about JSON and Javascript

Question

I am trying to create a correspondence management system that generates the reference of the same based on the last ID, and current date, I am using HTML, PHP, JAVASCRIPT, using the attribute Blur of javascript when I click outside the sender field automatically the reference field must be filled in my function has been working normally when running it on localhost with HTTP UNSAFE

However when I run it on a server with SSL certificate (Cpanel or others) this is HTTPS it does not automatically generate the reference provided by my function

I don’t know if it has anything to do with my JSON or Javascript, Below is the front code of my form

<script type="text/javascript">
                      $(document).ready(function(){
                        $("input[name='remetente']").blur(function(){
                          var $referencia1 = $("input[name='referencia1']");
                          var $referencia = $("input[name='referencia']");
                          $.getJSON('function.php',{ 
                            remetente: $( this ).val() 
                          },function( json ){
                            $referencia1.val( json.referencia1 );
                            $referencia.val( json.referencia );
                            $referencia = ( json.referencia )
                            Swal.fire({
                              icon: 'info',
                              title: 'Sua Referência: '+$referencia,
                              text: 'ANOTE! não modifique o campo referência',
                            });
                          });
                        });
                      });
                      </script>
                    <form method="POST" action="ad_correspondencia.php" enctype="multipart/form-data">
                        <div class="card-body">
                            <div class="row">
                                <div class="col-md-4 form-group">
                                    <label for="exampleInputEmail1">Assunto</label>
                                    <input required type="text" required class="form-control" name="assunto" id="exampleInputEmail1" placeholder="Título da Correspondência">
                                </div>
                                <div class="col-md-4 form-group">
                                    <label for="exampleInputEmail1">Remetente</label>
                                    <input required type="text" required class="form-control" name="remetente" id="exampleInputEmail1" placeholder="Entidade que envia">
                                </div>
                                <div class="col-md-4 form-group">
                                    <label for="exampleInputEmail1">Referência</label>
                                    <input required type="text" class="form-control" disabled name="referencia" id="exampleInputEmail1" placeholder="Nº de Referência">
                                    <input required type="hidden" class="form-control" name="referencia1" id="exampleInputEmail1" placeholder="Nº de Referência">
                                </div>
                            </div>

This is the code of my function (Function.php) that it should call

<?php
include_once("../conexao/conexao.php");

function retorna($remetente, $connection){
    $data = date('dmy');

    $consulta_id = "SELECT * FROM correspondencias";
    $resultado_id = mysqli_query($connection, $consulta_id);
    while($ids = mysqli_fetch_assoc($resultado_id)) {
        $ultimo_id = $ids['ID'] + 1;
    };

        $valores['referencia'] = $ultimo_id.'ESP'.$data;
        $valores['referencia1'] = $ultimo_id.'ESP'.$data;

    return json_encode($valores);
}

if(isset($_GET['remetente'])){
    echo retorna($_GET['remetente'], $connection);
}
?>

the interesting thing is that even in HTTPS when I run directly this code it presents me the data returned in JSON

So I don’t know exactly where the error is, remembering that I’m starting in the area of programming I’m still beginner!