You can tell if it is a secondary lottery by reading the offer description carefully.
A look at the general terms and conditions, the legal notice and the information on the licence can also help.
If you find phrases such as: “Place bets on the results of state and international lotteries”, it is an illegal secondary lottery.
Even if participation is significantly cheaper than with other well-known providers, you should be suspicious.
Thanks to the official white list of the Saxony-Anhalt State Administration Office, you can check whether the provider is in possession of a German gambling licence.
If the provider is not on the list, it is illegal gambling.
In such a case, you are not entitled to the payment of your winnings.