请帮我调试条带错误

错误：[16-May-2018 22:16:06 UTC] PHP致命错误：未捕获的异常'Stripe \ Error \ InvalidRequest'，消息'无效的源对象：必须是字典或非空字符串 . 请参阅https://stripe.com/docs上的API文档，位于/home/autravelservice/public_html/wp-content/plugins/ats/libraries/stripe-php-6.0.0/lib/ApiRequestor.php:120，来自API请求'req_6uGybuHR3adjqW'

请看我的代码有什么我做错了吗？

// Set your secret key: remember to change this to your live secret key in production
        // See your keys here: https://dashboard.stripe.com/account/apikeys
        \Stripe\Stripe::setApiKey($sk);

        // Token is created using Checkout or Elements!
        // Get the payment token ID submitted by the form:
        $token = $payment_details['token'];
        //echo 'pay:' . $pay_amount;

        // Create customer:
        $i = 0;
        foreach(get_field('applicant', $post_id) as $applicant) {
            if($i++ == 0) {
                $applicant_details = $applicant['applicant_details'];
                $contact_details = $applicant['contact_details'];


                $name_first = $applicant_details['first_name'];
                $name_last =  $applicant_details['last_name'];
                $email = $contact_details['email'];

                $user_info = array("First Name" => $name_first, "Last Name" => $name_last);

                $customer = \Stripe\Customer::create(array(
                    "email" => $email,
                    "card"  => $token,
                    "metadata" => $user_info
                ));

                // Charge the user's card:
                $charge = \Stripe\Charge::create(array(
                    "customer" => $customer->id,
                    "amount" => $pay_amount,
                    "currency" => "usd",
                    "description" => "Australian Travel Service"
                ));
            }
        }   
        if($charge->status == 'succeeded') {
            $counter = range(1, 5);
            $counter= shuffle($counter);
            $orderid = 'AUS-CU-' . date('Ymd') . $post_id . $counter;
            echo '<input type="hidden" name="orderid" id="app_order_id" value="'.$orderid.'">';
            echo '<input type="hidden" id="applicant_count" value="'.$applicant_count.'">';
            echo '<input type="hidden" id="processing_type" value="'.$processing_fee_type[0].'">';
            echo '<input type="hidden" id="order_total" value="'.$pay_amount.'">';
            appFormAdminMail($post_id, $orderid);
            acf_form(array(
                'id' => 'survey-form',
                'post_id' => $post_id,
                'field_groups'  => array(158),
                'return' => './survey-thank-you/?record=%post_id%',
                'submit_value' => 'SUBMIT SURVEY',
                'html_submit_button' => '<button type="submit" class="acf-btn red-btn rounded-btn">%s</button>'
            ));
        } else {
            echo 'Payment error...';
        }