Response to custom POST request with invalid JSON body is an HTML error page

Example request: 
```
curl -X POST -H "Content-Type: application/json" -d "{ 'text': 'Hi' }" https://some-api.200ok.app/some-custom-route
```

Response: 
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Error</title>
</head>
<body>
<pre>Bad Request</pre>
</body>
</html>
```