I have a custom payment module where I need a controller for callback to get notified about the payment, but the payment service only gives me the error that the response contains html. Also, in the controller action I log every request and there aren't any requests from the callback service coming in. When I cann the exact same URL manually in the browser, everything works as expected and the callback also works fine with a simple test php file, only with Magento controllers it doesn't. I just don't understand why I don't get the request. Any ideas?
Is it hosted on a local server or hosted on a server where the site is reachable?
http://localhost or any local network address is just unreachable from outside.