The API we provide programmatic access to Online Live Support features and data. In designing the API, our goal was to make it simple, intuitive, and predictable. The standards used in this API are widely accepted
We use POST HTTP request instead of GET is because it has no restrictions on data length. Thus, the output can contain long sentences that returned by the API.
POST supports binary data type as well. Hence the possibilities of user uploading images to change their logo.
For security concern, POST is a little safer because the parameters are not stored in browser history and web server logs unlike GET.
By using POST, the URL will remain clean because the data will not be displayed in URL.