finally found the very easy solution. It seems that Huawei blocks the local filesystem on the phone if the device is connected to the computer. Because of this, the SDK Tester cannot read the amazon.sdktester.json File. And this is finally the reason why I did not receive any IAP-Products.
So if it fails on your current phone. Be sure to check if you cannot access the files in the phones fileexplorer. If not change the phone and it will work.