Parameters:

- `topic` (required): Address for the message, e.g. `myAddonRootVar/function1/myTopic/`. The same topic must be used when retrieving the message.
- `payload` (required): The message to send, e.g. `"test message"`.
- `token` (optional): Key string. If provided, the exact same string must be supplied when retrieving the message.
- `lifetime` (optional): How long the message is available, in seconds. Default 8 hours, maximum 7 days (adjustable for dedicated installations).