WordPress contact form using the API

contact.js

(function($) {
    $(".submit-contact-form").on("click", function(e) {
        e.preventDefault();

        $.ajax({
            url: theme_data.site_url + 'wp-json/send-contact-form/v1/contact',
            method: 'POST',
            data: data
        }).done(function(data){

        }).fail(function(data){

        });
   })
})(jQuery);

functions.php

<?php
//Register endpoint
function ath_endpoints()
{
    register_rest_route('send-contact-form/v1', '/contact/', array(
        'methods' => 'POST',
        'callback' => 'send_contact_form'
    ));
}
add_action( 'rest_api_init', 'ath_endpoints' );

handle-submit.php

<?php
define("API_KEY", "apikey");
define("DOMAIN_NAME", "domain.com");

function mailgun_send( $to, $subject, $message )
{
  $curl = curl_init();
  curl_setopt( $curl, CURLOPT_HTTPAUTH, CURLAUTH_BASIC );
  curl_setopt( $curl, CURLOPT_USERPWD, 'api:key-'.API_KEY );
  curl_setopt( $curl, CURLOPT_RETURNTRANSFER, 1 );
  $plain = strip_tags( nl2br( $message ) );
  curl_setopt( $curl, CURLOPT_POST, true );
  curl_setopt( $curl, CURLOPT_URL, 'https://api.mailgun.net/v3/'.DOMAIN_NAME.'/messages' );
  curl_setopt( $curl, CURLOPT_POSTFIELDS, array(
      'from' => '<mailgun@'.DOMAIN_NAME.'>',
      'to' => $to,
      'subject' => $subject,
      'html' => $message,
      'text' => $plain
  ) );
  $response = json_decode( curl_exec( $curl ) );
  $info = curl_getinfo( $curl );
  if( $info['http_code'] != 200 )
  {
      die( "Email failed to send" );
  }
  curl_close( $curl );
  return $response;
}

function send_contact_form( WP_REST_Request $request )
{

    $form_location = $request['form_location'];
    $full_name = sanitize_text_field( trim( $request['full_name'] ) );
    $email     = sanitize_email( trim( $request['email'] ) );
    $body      = sanitize_text_field( trim( $request['body'] ) );
    $errors = [];
    if( empty( $full_name ) )
    {
        $errors["full_name"] = "Name is required";
    }
    if ( empty( $email ) || ! filter_var( $email, FILTER_VALIDATE_EMAIL ) )
    {
        $errors["email"] = "Valid Email is required";
    }
    if ( empty( $body ) )
    {
        $errors["body"] = "Message is required";
    }
    $message = "<h4>From: ".$full_name."</h4>";
    $message .= "<h4>Email: ".$email."</h4>";
    if( $form_location == "get-coverage-modal" || $form_location == "get-coverage-page" )
    {
        $subject      = "Get Coverage";
        $company_name = sanitize_text_field( trim( $request['company_name'] ) );
        $interest     = sanitize_text_field( trim( $request['interest'] ) );
        $message .= "<h4>Company: ".$company_name."</h4>";
        $message .= "<h4>Interest: ".$interest."</h4>";
    }
    if( $form_location == "contact-page" )
    {
        $subject = sanitize_text_field( trim( $request['subject'] ) );
    }
    if( $form_location == "company-page" )
    {
        $subject      = "Wrong/missing information on a company";
        $company_name = sanitize_text_field( trim( $request['company_name'] ) );
        if ( empty( $company_name ) )
        {
            $errors["company_name"] = "Company name is required";
        }
        $message .= "<h4>Company: ".$company_name."</h4>";
    }
    $message .= "<p>".$body."</p>";
    if( count( $errors ) > 0 )
    {
        return new WP_Error( 'contact_form_errors', $errors, array( 'status' => 422 ) );
    }
    $headers = array('Content-Type: text/html; charset=UTF-8');
    wp_mail( "email@email.com", $subject, $message, $headers );
    mailgun_send( "email@email.com", $subject, $message );
    return "success";
}