What size screenshots should be used for IAPs ( In app purchases ) for Mac apps?

In the official docs I found this:

A screenshot of the product as it appears on the device. This screenshot is used for Apple’s review only and is not displayed on the App Store. Screenshots requirements are outlined below: iOS: at least 640 x 920 pixels. tvOS requires 1920 x1080 pixels. macOS requires 1280 x 800 pixels.

Source: https://help.apple.com/app-store-connect/#/dev84b80958f

Interesting enough I just tried with a 640px (width) by 920px (height) screenshot for Mac IAP and everything is fine. Make sure you have no alpha-channel, but this gives another error.

I would like to add to the accepted answer because regurgitating the documentation does little to resolve actual problems.

After taking a screen shot of the app on my device for in app purchase review and it still didn't work, I did some investigating.

After you attempt to upload a screen shot and see the error to upload a valid size, you can open the browser inspector to see the error details. The image MUST be one of these dimensions: accepted resolutions found in console error

Something else I didn't realize is when taking screen shots with command-shift-4 on macbooks, when you hold it down for the drag you can see the actual dimensions of the screen shot you are taking, but for some reason it saves it as DOUBLE the size. I ended up taking a screen shot where the cross hairs of the screen shot say 320 x 480 resulting in a saved png of 640x960. It has to be one of the pre set sizes in order for image upload to accept it.

After banging my head on a wall for a couple hours I figured this out, so I hope this helps others .