How to complete Alleways Maps?

Hello everyone,

I entered PoE's Endgame for the first time ever, I am not new to PoE itself, but to all it's Late/Endgame mechanics, so I am totally new to Atlas as well.

I completed almost 20 maps so far, but I did not get any Atlas Points to improve my Atlas Tree further.

I struggle with completing the Bonus Objective, which is afaik killing the Map Boss, in this case, Calderus, which is the Boss of the Alleways Maps.

Well, I did that multiple times now, even cleared the whole map without any Monster remaining, but I still do not get the Bonus Objective completed.

I talk about a white Tier 1 standard map, no further modifications to it or anything esle.

So, what do I do wrong here?

Thanks for the help guys!

For Atlas completion, Tier 1 to 5 maps need to be magic/blue, not plain white.