It is possible to use attachments with the Jinja connector as follows:
{
"attachments":[
{
"name":"A very black small image",
"content":"iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+A8AAQUBAScY42YAAAAASUVORK5CYII="
}
]
}
content takes a file which must be encoded as a base64 string.
Attachments can also be part of the Jinja template itself:
<html>
<body>
<object type="attachment" name="A very black small image" content="iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+A8AAQUBAScY42YAAAAASUVORK5CYII="></object>
</body>
</html>