Do screenshots for an App Store submission have to show part of a device in them or can they just be the screen?

I have a new app which has never been publish, but has been approved and it has a status of "Pending Developer Release". I am trying to generate promo codes for it, but keep getting error: "Can't Generate Promo Codes We're having trouble generating the codes. Please contact App Store Developer Support for assistance." When I click the link it just says "Something went wrong." I have messaged Apple for help, but have not had any response yet. The Apple documentation says the app can be in "Pending Developer Release" and does not have to be "Ready for Sale". Anyone know why this is failing? TIA.