How to create an Array with hand picked Blocking Volumes or tell Trace to ignore them otherwise

Hello Community,

I am a absolute Noob, therefore my question might be fairly stupid.
I try to feed the ignore pin of my LineTraceByChannel with an Array of Blocking Volumes.
If I set up the Variable with type Blocking Volume, and choose Array, I should be able to fill the Array slots via drop down list or by picking it from the viewport.
The drop down list is showing all my Blocking Volumes, but if I choose one, it just goes closes the drop down list without taking the choice.
When I try to pick from viewport, my picker indicates that the volume is valid for picking, but still it will not take the choice into my array.

Also, I tried to use tags on these volumes and used GetAllActorsWithTag to feed the ignore pin of the Trace, but no success.

I did not find any tutorial describing this setup, so I guess there are better ways to tell my trace what Blocking Volumes to ignore?

Thanks for your support