You have to precomposed it and then do your mask.
The other option is to put the mask on the other layer.
The last option is to use the track matte.
You just have the wrong workflow, that's all.
You have to precomposed it and then do your mask.
The other option is to put the mask on the other layer.
The last option is to use the track matte.
You just have the wrong workflow, that's all.