Masking works in the opposite way from the way it works in Illustrator. The objects being used as the mask need to be at the very bottom of the objects that you wish to mask. Place your object at the bottom of the layer containing the objects you need to mask OR place the mask object on its own layer BELOW those layers/objects you wish to mask and THEN SELECT the mask/mask layer and the objects/layers that you wish to be masked.
To create a clipping mask, follow these steps:
In the Puppet panel, arrange the layers in a way that the layer with the mask is placed below the layers you want to mask.
Select the layers you want to mask and choose Puppet > Create Clipping Mask (Cmd+Option+G (MAC) or Ctrl+Alt+G (Windows). Multiple selected layers can be masked if they are adjacent in the layers list and don’t include the last layer in a group.
Note:If a layer is inserted between layers in a clipping mask, it becomes the base layer for the layers above it and is not clipped.
The name of the base layer in the mask is underlined in the Puppet panel and the names of the overlying layers are indented. The overlying layers also display a clipping mask icon.