As far as I know, there's no ads platform for apple watch at the moment. But if I add advertising screens in manually, does it have no problem?
Advertising screen in Apple Watch
IMO there should not be a problem. But it will not be paid ads I guess.
From the App Store Review Guidelines:
3.1.7 Advertising: Display advertising should be limited to your main app binary, and should not be included in extensions, App Clips, widgets, notifications, keyboards, watchOS apps, etc.
Apple Watch apps are designed for interactions that take just a few seconds. If I’m launching my coffee loyalty app on my watch so I can bring up my member barcode to scan at the register, I’m going to be frustrated if I have to dismiss an ad to get to it.
If you have special offers for your customer and want them to be viewable in your Apple Watch app, consider putting them inside your app’s navigation.
One more note based on the screenshot you’ve posted: 1D barcodes (like the one in the screenshot) may be difficult to scan when displayed on Apple Watch. Consider using a 2D code instead. Make sure to test scanning the code with the same scanner hardware that’ll be used at the actual point of purchase, using multiple Apple Watch sizes (especially our smallest display, Apple Watch Series 3 38mm).