It's possible to add attachments to message: for example, image, audio file or video file. We don't have any restrictions here - you can attach any type of file.
To send a message with attachments you should use the same way as you send regular message with text, but add to it an attachment object. Attachment can be:
A file in Content module: iOS example. This is a way we recommend.
A file in Custom Objects module: iOS example
Can be an url to any file in Internet
To send a message with attachment you should upload a file to Content module, Custom Objects module using sample above or use an url to any file in Internet. Then you should incorporate an ID to file to message.
For example, we use Content module to store attachments. Next snippets show how to upload a file to Content module and send it as an attach: