My Dynamic Ads campaign is not delivering at all (on Instagram)
This can be due to your original product images being too small. Despite Image Templates producing big enough images, Facebook requires the original image, defined in the Image Link field of the catalog to be big enough; for Instagram, at least 600px by 600px (source).
Preferred solution: if possible, provide bigger images in the Image Link field defined in your feed settings.
Alternative solution: it is possible to place your original image URL in another catalog field, and use Smartly.io Image Templates to produce a larger version of that image for the Image Link field. This is the last resort, requires some hacking, and might be unreliable. Ask your account manager for help.
I can't access a nested item in a JSON feed
You can access nested items in a JSON feed by using a “/“ to denote moving to the next layer or 'level'. For instance, if you had an object like the one below, you could access the “imageLink” by using the syntax houses/0/floors/0/rooms/1/imageLink. The numbers in this situation denote the array position you are trying to access, starting from 0. It translates to, "In the first entry of the "houses" array, in the first floor item of the "floors" array, in the second room of the "rooms" array, return the imageLink"