当数据来自MySQL时，Typeahead不会从PHP文件中给出响应

我试图从PHP文件（JSON数据）中获取自动完成（typeahead）的数据。然而，只有当我复制粘贴JSON数据并从PHP文件中回显它时，它才起作用。如果我使用string builder或array_push（）函数生成完全相同的JSON数据，那么它就不起作用。 数据是巨大的，我比较了两个PHP文件的输出；完全一样

工作代码 echo json_编码（数组（“沃尔沃”、“宝马”、“丰田”）； 此PHP文件的输出：[“Acura”、“Audi”、“BMW”]

不起作用 来自MySql的数据得到了回应 此PHP文件的输出：[“Acura”、“Audi”、“BMW”]

JAVASCRIPT

$.typeahead({
input: '.js-typeahead-car_v1',
minLength: 1,
order: "asc",
offset: true,
hint: true,
source: {
    car: {
        data: ["My first added brand", "M1 added brand at start"],
        ajax: {
            type: "POST",
            url: "car_v1.php",
            data: {
                myKey: "myValue"
            }
        }
    }
},
callback: {
    onClick: function (node, a, item, event) {

        console.log(node)
        console.log(a)
        console.log(item)
        console.log(event)

        console.log('onClick function triggered');

    },
    onSubmit: function (node, form, item, event) {

        console.log(node)
        console.log(form)
        console.log(item)
        console.log(event)

        console.log('onSubmit override function triggered');

    }
}
})

HTML

<form id="form-car_v1" name="form-car_v1">
<div class="typeahead__container">
    <div class="typeahead__field">
        <div class="typeahead__query">
            <input class="js-typeahead-car_v1" name="car_v1[query]" placeholder="Search" autocomplete="off">
        </div>
        <div class="typeahead__button">
            <button type="submit">
                <i class="typeahead__search-icon"></i>
            </button>
        </div>
    </div>
</div>

header('Content-Type: application/json');

echo json_encode(
array(
    "Acura", "Audi", "BMW", "Buick", "Cadillac", "Chevrolet", "Dodge", 
    "Chrysler", "Ford", "GMC", "Hyunday",
    "Infinity", "Jaguar", "Jeep", "Kia Motors", "Land Rover", "Lexus", 
     "Lincoln", "Mazda", "Mercedes-benz",
    "Mitsubishi", "Nissan", "Pontiac", "Porsche", "Saab", "Saturn", "Scion", 
     "Subaru", "Suzuki", "Toyota",
    "Honda", "Hummer", "Mercury", "Mini", "Volkswagen", "Volvo"
  )
 );