Hi,
In the "notif_payment" parameter of your notify URL, you need to enter the name of the plugin which probably is not ogone.
Also, that URL needs to be available by anyone else (so your website needs to be online, the website shoudl not be in maintenance, and not protected by a htaccess authentication, and the menus should be accessible by all the uer groups on your website.
Then, the payment gateway will be able to send his payment notification to that URL and if you echo some text at the beginning of your plugin's onPaymentNotification function and then return, you should see it in the payment log file available in the configuration of HikaShop.