Why can't I list products from dropship platforms onto multiple marketplaces?

[GreenMtn]

I signed up for shopify to dropship across several markets like amazon and walmart, ebay etc. The problem is I can't get ANYTHING to work on this site, I cant list a single product from here on any other marketplace, all I ever get is infinite loading screens, error messages, or a loop back to "0 listings available"

I have my amazon and ebay accounts linked through marketplace connect but I can't list anything from here on them.

I can get products onto my shopify products list but can't get them listed for sale. I've spoken to support for both shopify and the apps (salestio, marketplace connect) and they always say "it should just work, oh it doesn't? thats weird" the help articles are just vague descriptions of what dropshipping is or they point to buttons/features that don't show up.

can anyone clearly tell me how do you take a product from your shopify products and get it listed for sale on amazon/walmart?

I already have 4 online stores, shopify is 1000 times more buggy/convoluted than all of them, they all took about 1 hour to get up and running but I've spent countless hours on this platform and can't even list one item.