Using Pie Charts to count amount of defined Strings

Hi there

I am currently trying to setup a pie chart which should count the amount of a certain String in a given data set. My value expression uses the Group by function with exact match on the String and a :count operator. Still the chart displays each String differently and does not count the same String together. Therefore every entry just has a count of one instead of being grouped together. Has anyone any experience? Is this even solvable with the Bubble Pie Chart Plugin?

Thanks and kind regards

Make sure to put the count inside of the aggregation, then use format as text to comma separate the values shown below: