Message type, The allowed values are "text", "image", "share_link" If the value is image, then an image with the field image needs to be submitted through post.
Example:
image
to_uid
integer
required
Opposite user ID.
Example:
31
message
string
optional
Message Content.
Example:
test message
image
file
optional
When the message type is image, an image needs to be uploaded. The image size must be less than 5mb. There are several allowed mimes: 'image/gif', 'image/jpg', 'image/jpeg', 'image/png'