Can't send message via matrix?

I am using the latest version of ntfy, and am on Ubuntu 18.04 LTS (in case that's useful info). I am trying to use ntfy to send me a message on matrix when the command finishes. I followed the docs and created a ntfy.yml in ~/.config/ntfy/ntfy.yml. I followed the template with the filling text in the yml:
```
matrix:
url: matrix.org
roomId: "[myroomid]"
token: "[mytoken]"
```

But when I run `ntfy send test` I only get the desktop notification. Is there something wrong the yml?

I also ran `ntfy -b matrix send test` and got the following result:
```Traceback (most recent call last):
File "/usr/local/bin/ntfy", line 11, in
sys.exit(main())
File "/usr/local/lib/python2.7/dist-packages/ntfy/cli.py", line 367, in main
**dict(args.option.get(None, [])))
File "/usr/local/lib/python2.7/dist-packages/ntfy/__init__.py", line 31, in notify
backend_config.update(kwargs)
AttributeError: 'NoneType' object has no attribute 'update'
```