Hi @Mehl,
Here is a tip for you, please translate the error message in English next time. Thanks for your cooperation.
Could you please show me how you format the text into currency, show me the Default property of the data card value?
You mean you want to do calculation between a currency value and number value, right?
Firstly, you should format your currency into number value, then calculate with these two number values.
Just modify your formula as below:
Value(DataCardValue25.Text)*Value(DataCardValue19.Text)