German Rentenmark was created in 1923.

Please check the date and the spelling. That's "Zwei Rentenmark", and it's "Deutsche Rentenbank".

Regarding the date rentenmarks were issued under the Weimar Republic which ended when Hitler seized power in 1933. German coinage was then denominated in Reichsmarks, so you could not have a rentenmark coin from the Nazi era.

Please post a new question with the coin's corrected date.

Deutschmark

or Rentenmark before that

It is generally a matter of opinion which of Stresemann's policies was his most successful but some stand out more than others.

Stresemann's biggest achievements were stabalising the German economy and subsequently the political scene and the admitance of Germany into the League of Nations in 1926.

The most important of his policies was the issuing of the new currency: the Rentenmark. The Rentenmark restored faith in the German economy at home and abroad. It boosted industry and allowed Germany to trade with other nations again now that the hyperinflation crisis and the worthless curreny were gone. The Rentenmark restored such confidence in the Germany economy that American banks were willing to invest money in 800 million marks of loans to Germany businesses in the 1924 Dawes Plan. The Dawes Plan further stabalised the German economy and political scene and further brought trust to Germany from abroad - allowing a successful run of forein policies.

it helped stabilise germanys economy by keeping hyperinflation under control