-If the required API is not enabled, enable it. Then wait for about 15 minutes, clear the HMS Core (APK) cache on the test phone, and check whether sign-in can be successful.
-If the API has been enabled, the possible cause is that an exception occurs when the API is enabled, which rarely happens. As a result, Huawei server does not receive the synchronized API enabling request. In this case, you can manually disable the API and then enable it again to trigger message synchronization. Similarity, clear the HMS Core (APK) cache, wait for 15 minutes, and perform the test again.
To clear the HMS Core (APK) cache, go to Settings > Apps > Apps > HMS Core on your test device, and clear the cache.
I tried the latter solution, and site kit worked properly.