UPDATE:
I got it to work.
The JSON needs to have the media_type, image_url and video_url exactly written like that.
{
“slides”: [
{
“fileName”: “slide1”,
“image_url”: “URL1”,
“media_type”: “IMAGE”,
“video_url”: “URL1”
},
{
“fileName”: “slide2”,
“image_url”: “URL2”,
“media_type”: “VIDEO”,
“video_url”: “URL2”
}
]
}
On the Aggregator part select Target Structure → Custom, mark the parameters and nothing more (There is another variable that is user_tag (array with tags) that can be added to improve this mapping if you need that).
After running it I got an error 2207026 on Instagram Module but it was that I was sending a 9:16 video. The requirement for Carousel videos are 1:91 to 4:5 aspect ratio
I fixed my video and my mixed Images and Video Carousel, from a JSON file is posted 
Here is a birds-eye view of the full combination for reference (I am starting and ending in a Google Sheet to mark the post as Posted)
