how to post restfull api to database via codeigniter with explode function?

[url=https://stackoverflow.com/posts/63764218/timeline][/url]

rest api request, type:post, request body:

Code:

{"data":"albert amstrong,18838327"}

If you see, i want to separate json object by "," and post to columns in my database...
my database name is data
how to make it as below.....

Code:

-----------------------------------
|id   | name           | number   |
-----------------------------------
|  1  |albert amstrong | 18838327 |
|     |                |          |
|     |                |          |
|     |                |          |

my php code

Code:

public function index_post()
{
        $data = $this->post('data');
        $data = json_decode($data);
        $sth=$this->db->prepare('INSERT INTO kontak SET name=?, number=?');
        $sth->execute(array_map('trim', explode(',', $data->data)));
}          

error message:

Code:

    <h4>An uncaught Exception was encountered</h4>

<p>Type: Error</p>
<p>Message: Call to undefined method CI_DB_mysqli_driver::prepare()</p>
<p>Filename: /home/dokdafta/domains/donkeys.xyz/public_html/wa/application/controllers/api/Okaja.php</p>
<p>Line Number: 42</p>