I get a  HTTP request failed! HTTP/1.1 400 Bad Request error while trying to create a hosted page for new subscription using Hosted Page API

Here's my code:

2. $data = array(
3. 'customer'=>array('display name'=>'Mr. Hash Tiwari','first_name'=>'Tarun','last_name'=>'Tiwari','email'=>"tarun@noemail.com",'mobile'=>'99999999999'),
4. 'plan'=>array('plan_code'=>'Small'),
5. 'custom_fields'=>array('variant'=>'Chicken'),
6. 'reference_id'=>'2222222'
7. );
8. 
   
9. $data = json_encode($data);
10. 
    
11. $context = array(
12.   'http'=>array(
13.     'method'=>"POST",
14.     'header'=>"Content-Type: application/json;charset=UTF-8\r\n" .
15. "Content-Length: ".strlen($data)."\r\n".
16. "X-com-zoho-subscriptions-organizationid: 639344623\r\n" .
17. "Authorization: Zoho-authtoken xxxxxxxxxxxxxxxxxxxxxxxxx\r\n",
18. 'content'=>$data
19. )
20. );
21. 
    
22. $context = stream_context_create($context);
23. // Open the file using the HTTP headers set above
24. $file = file_get_contents("https://subscriptions.zoho.com/api/v1/hostedpages/newsubscription", false, $context);
25. 
    
26. echo $file;