Simple MailJet API v3 email sender in PHP

SimpleMailJetSender.php

<?php

class MailJetAPI{
    /*
    * Simpel MailJet mailer with the v3 API
    */
    
    private const BASE_URL = 'https://api.mailjet.com/v3.1/send';
    private $key;
    private $secret;

    public function __construct($user_key, $user_secret){
        # Mailjet credentials
        $this->key = $user_key;
        $this->secret = $user_secret;
    }

    public function sendEmail( $subject, $message, $to_mail, $from_mail, $from_name = '' ){
        # Send MailJet email

        $ch = curl_init( self::BASE_URL );
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE );
        curl_setopt($ch, CURLOPT_USERPWD, $this->key . ':' . $this->secret );

        # Message content
        $msg = ['Messages' => [['From' => ['Email' => $from_mail,'Name' => (empty($from_name) ? $from_mail : $from_name)],'To' => [['Email' => $to_mail]],'Subject' => $subject,'HTMLPart' => $message]]];
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode( $msg ) );

        # Headers
        $headers = ['Content-Type: application/json'];
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

        # Execute and check response code
        $result = curl_exec($ch);
        $httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        if ( curl_errno($ch) ) return curl_error($ch);
        curl_close($ch);
        return json_decode( $result, FALSE );
    }
}

# MailJet mailer
$mailer = new MailJetAPI('ab12cd34ef56gh78ab12cd34ef56gh78','87hg65fe43dc21ba87hg65fe43dc21ba');
# Send email
$mail_result = $mailer->sendEmail('Hello New User', '<b>Welcome to our Service</b>', 'newuser@example.com', 'admin@domain.com', 'The Admin');

?>