@Alohaa I don't know why it is that you don't have the button but I did get your file.
Looking at sections through the objects it appears to me that you probably started out by drawing all of the features for each object in 2D and then started extruding face upward. This results in missing faces as well as internal faces.
![Screenshot - 7_7_2024 , 7_40_48 AM.png](/assets/uploads/files/1720356309264-screenshot-7_7_2024-7_40_48-am.png)
![Screenshot - 7_7_2024 , 7_41_02 AM.png](/assets/uploads/files/1720356317357-screenshot-7_7_2024-7_41_02-am.png)
Your objects can be cleaned up but it would probably be easier just to start over modeling it all correctly. If I were modeling these parts I would model them in a way that is very similar to the way filament gets laid down by a 3D printer. Don't model features until you come to them in the height. Don't spend so long thinking in 2D.
There are also a number of stray edges. And what is your intend for the rim of the top piece? Currently you have a zero thickness face between the wall of the box and the surrounding rim. That won't work as it is. Also. What's the story with the text? As it is, that won't print.
Edit to add: I recorded a silent video showing a way to model the bottom part of the enclosure. Note that I did not outline the sides of the box or the raised screw bosses until after the bottom thickness was created. Only the features that would be outlined on the build plate of the 3D printer are modeled before the thing becomes 3D.
https://flic.kr/p/2q2Jwda
Another thing I did and have talked about in previous threads here is set units to Meters and model as if millimeters are meters. This allows the use of more segments for small radius curves.
I finished the box parts as solids.
![Screenshot - 7_7_2024 , 8_57_35 AM.png](/assets/uploads/files/1720360883227-screenshot-7_7_2024-8_57_35-am.png)
HERE IS THE SKETCHUP FILE OF MY VERSION OF YOUR MODEL
Kasten fur Manaboard~.skp