I can't upload using the API

1. $url = https://crm.zoho.com/crm/private/xml/Contacts/uploadFile?authtoken=###&scope=crmapi&id=###
2. $ch = curl_init();
3. curl_setopt($ch, CURLOPT_HEADER, 0);
4. curl_setopt($ch, CURLOPT_VERBOSE, 0);
5. curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
6. curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
7. curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
8. curl_setopt($ch, CURLOPT_URL, $url);
9. curl_setopt($ch, CURLOPT_POST, TRUE);
10. $post = [];
11. $post['id'] = $id;
12. $post['content'] = '@'.realpath($file);
13. curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
14. $response = curl_exec($ch);

var_dump($response);

1. <?xml version="1.0" encoding="UTF-8" ?>
2. <response uri="/crm/private/xml/Contacts/uploadFile"><error><code>4424</code><message>Unable to process your request. Please verify whether you have provided proper file.</message></error></response>

I have been trying to everything for a day, please help.