What could I have done wrong when updating Complications from my App?

Hello,

I have an app that takes data from a weather station API and dispkays it in a Widget. I now wanted to extend this to a Complication  to show it on watchfaces. I have defined two Complications in the resource XML file, and I am using the Complication.update(0,{value=>"This is a test"}); method, but with my data as String variables onstead of staric text, whenever I get new data.

However, in the Simulator, it always displays "--", which is a value I have once put into a Complication but since then it should have updated it countless times.

What do I have to do in order to make it work?

Best regards 

Aaron