Why is sql query throwing an error?

Question

PHP

Hello! I am writing a communication module between the administrator and the user, messages are stored in the database. Now I decided to add pagination to them, I wrote the following query to the database:

public function getAllMessages($data) {
 
$sql = $this->db->query("SELECT * FROM " . DB_PREFIX . "message WHERE status = 1 ORDER BY date_added DESC");
 
if (isset($data['start']) && isset($data['limit'])) {
if ($data['start'] < 0) {
$data['start'] = 0;
}
 
if ($data['limit'] < 1) {
$data['limit'] = 10;
} 
 
$sql .= " LIMIT " . (int)$data['start'] . "," . (int)$data['limit'];
} 
 
$query = $this->db->query($sql);
 
return $query->rows;
}

but swears at an incorrectly composed request:

Unknown: Object of class stdClass could not be converted to string in /catalog/model/contact/message.php on line 28
Notice: Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LIMIT 0,10' at line 1
Error No: 1064 LIMIT 0,10 in /system/library/db/mysqli.php on line 40
Notice: Trying to get property of non-object in /catalog/model/contact/message.php on line 33

I can't figure out what could be the problem?