The first issue here is your returning HTML not JSON data, so the error is related to your code trying to parse the HMTL into a JSON array, which is not right.

Either change your javascript to reflect that you are responding with HTML or if that is a mistake, make sure your response is correct JSON.

I can also see from your inspect that the page you are testing has a PHP error, this might be related to the JSON issue if the same error is being spat out just before the JSON data, you can check this by looking at the XHR requests tab and you should be able to see your ajax request and response data.