I am very late but if some one working on SLIM to make rest api and getting same error can solve this problem by adding below line as:
<?php
// DbConnect.php file
class DbConnect
{
//Variable to store database link
private $con;
//Class constructor
function __construct()
{
}
//This method will connect to the database
function connect()
{
//Including the constants.php file to get the database constants
include_once dirname(__FILE__) . '/Constants.php';
//connecting to mysql database
$this->con = new mysqli(DB_HOST, DB_USERNAME, DB_PASSWORD, DB_NAME);
mysqli_set_charset($this->con, "utf8"); // add this line
//Checking if any error occured while connecting
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
//finally returning the connection link
return $this->con;
}
}