Codeigniter to Send form data to api url - php

Question

I have form (5 fields which includes 1 file attachment field), whose field's data I need to submit on db as well as send on api url.
If I put api url in action of form tag then form data being send successfully. BUT I can't add api url in action coz like this form will redirect to that api url by leaving the site.
So to avoid putting api url in action I used following code to send form data to api url.
/* Endpoint */
$url = 'http://url_here';
$tmpfile = $_FILES['image']['tmp_name'];
$filename = basename($_FILES['image']['name']);
$data = array(
'to' => $to,
'cc' => '',
'message' => $subject,
'attachment' => '#'.$tmpfile.';filename='.$filename,
'message' => $message
);
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
/* Define content type */
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type:application/json'));
/* Return json */
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
/* make request */
$result = curl_exec($ch);
/* close curl */
curl_close($ch);
echo $result;
This code giving this error.
{"timestamp":"2022-03-09T07:23:54.873+00:00","status":415,"error":"Unsupported Media Type","message":"","path":"/QRCodeGenerator/sendmail"}
While searching for solution, I also tried adding
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Accept:application/json'));
For Accept:application/json to work I did convert array into json using jason_encode(). But it was still giving same error.
Where I am getting wrong?
UPDATE
I tried this code also which I got from postman where api working fine.
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_URL => 'http://url_here/QRCodeGenerator/sendmail',
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => '',
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => 'POST',
CURLOPT_POSTFIELDS => array('to' => 'example#gmail.com','cc' => '','message' => 'This is test subject','body' => 'this is body msg','attachment'=> new CURLFILE('/path/to/file')),
));
$response = curl_exec($curl);
curl_close($curl);
echo $response;
But this is giving blank page. $response printing nothing.