This is exactly what I tell you
First Schedule on a list of image, from this WF, after the API response, Schedule on a list of the type of the API Response list (I don’t know the name, but you can see it in API Connector when you initialize your call)

If you need to merge them all in a single item, you may need to check to have enough time between each schedule on a list to avoid racing issue. But in most case, you will probably create one response for each image/array list item. You only need to have something to link them together (user or DB thing for example). This information should be provided in the first Backend WF in a parameters that will also be used in the second Backend WF when you schedule on a list.