Help with joint push pull

hello I really need some help with my 3D Modell
I don´t know what I’m doing wrong:
I´ve created an organic shape with the skin bubble tool and now I`m trying to give it some thickness with the joint push pull tool but it doesn’t work.
Can someone help me and explain what I’m doing wrong?
It works with the vector tool but not with the joint push pull tool

To get useful help you should upload your model (the .skp file), not just an image.

If it is less than about 15MB, drag and drop the file into your post, or if it’s bigger, upload it to a file sharing service like Dropbox, OneDrive, or WeTransfer and post a link. Make sure your upload is readable by others.

One first question: Is the model very small?