SQL Query Clicking on the image that brings the selected color inside the input

Question

I updated the server: the form has stopped working. The image fires an onclick, which switches the image on the form slide (this works); and informs the id/value of the selected color, which goes back inside the input 'Color' which is now only Loading...

below the input code:

<input type="image" name="mudador" value="6" src="...tenis.webp" onclick="if (!window.__cfRLUnblockHandlers) return false; javascript: exibir('01');">

of the script:

    $(document).ready(function(){
            $("input[name='variavel']").click(function(event){
                var nomePMG = $("input[name='nomePMG']");           
                $( nomePMG).val('Carregando...');

                    $.getJSON(
                        'function_PMG.php',
                        { idCliente: $( this ).val() },
                        function( json )
                        {
                                                    
        $( nomePMG ).val( json.nomePMG );                   }); }); });

and PHP

    <?php
        $con = mysql_connect('localhost', 'lojas178_ogj', 'gardalla270837');
            mysql_select_db('lojas178_PMG', $con);

        /** * função que retorna o select */
        function montaSelect()
        {
            $sql = "SELECT `idCliente`, `nomePMG` FROM `cliente` ";
            $query = mysql_query( $sql );

            if( mysql_num_rows( $query ) > 0 )
            {
                while( $dados = mysql_fetch_assoc( $query ) )
                {
                    $opt .= '<option value="'.$dados['idCliente'].'">'.$dados['nomePMG'].'</option>';
                }
            }
            else
                $opt = '<option value="0">Nenhum cliente cadastrado</option>';

            return $opt;
        }

        /**  * função que devolve em formato JSON os dados do cliente */
        function retorna( $id )
        {
            $id = (int)$id;

            $sql = "SELECT `idCliente`, `nomePMG`, `telefone`, `endereco`
                FROM `cliente` WHERE `idCliente` = {$id} ";
            $query = mysql_query( $sql );


            $arr = Array();
            if( mysql_num_rows( $query ) )
            {
                while( $dados = mysql_fetch_object( $query ) )
                {     
                     $arr['nomePMG'] = $dados->nomePMG;
                    
                }
            }
            else
                $arr[] = 'endereco: não encontrado';

            return json_encode( $arr );
        }

    /* só se for enviado o parâmetro, que devolve o combo */
    if( isset($_GET['idCliente']) )
    {
        echo retorna( $_GET['idCliente'] );
    }