Need Help DAX - Comparing Periods

Hi, 
Im quite new to Power Bi , i hope someone can help me with my topic.

I need help displaying 2 different periods of Data.

I get this error when trying to display my Measure

What do i want to do:

I just want to compare 2 periods of Data - one period is from 2021 - the other is from 2020.

What have i done so far :

1) I have imported tables from a MS SQL Database  - No direct query

The Table with the Data ( especially the clomn with the date ) looks like this.
All Data is in one Table.

2) i have set the displayed filters on the visual - so far so good - data displays right on the visuals

3)  now i want an additional column with data (comparison)  with the 2020 period data
As far as i know "measure´s" are the right thing to accomplish that.

4) My Measure looks like this: 

Measure = calculate(sum('Verkauf lvRechnungsposition'[fBruttoPreisGesamt]),DATEADD('Verkauf lvRechnungsverwaltung'[dErstellt],-3,YEAR))

Once i drop the measure into my visual i get the error above

I can not identify the error here, i dont know what i have done wrong.

I hope someone can give me a hint on this.
Thank you !
Mitsch