A face has no thickness, so it must be indicated on which side of the face the tool should be positioned.
If the machining is under the face, it means that its material side is reversed.
You must switch to Modeling stage. Then go to Surface -> “Others” and use the function "Normal inversion… ".
Click on the face and double click on the arrow so that it points to the right side of the face.
The machining will then be correct.