Hi Loco,
you need all of the parameters you get in in body → upload parameters from the initial API call to pinterest mapped in the next HTTP call. Its a total of 8 parameters and 1 video file you need to send. Here are a couple of screenshots to get you started on what it should look like:
The media_id you get as a response from the first API call module to pinterest. After the upload is done you can use it to make the post. I have a delay of 30 seconds between the upload call and the post call just in case.