Note that some API calls are PUT requests and others are POST. For example, to create audiences you need to PUT. To send notifications, you need to POST. I didn't know this subtle difference but it makes sense according to: https://stackoverflow.com/questions/630453/put-vs-post-in-rest
Also note that you can't have punctuation in the URL. For example, my app is called "Stocks++" but you need to leave off the "++" for it to work in the REST calls.