Problem with shell - Error

[system]

I get error creating shell. Please see what am I doing wrong

I have a Dynamesh,
I select InsertCylinder brush, draw it at the bottom of the object,
Masking>Clear
Thickness 2
Create Shell

I get error: Create shell requires submesh insert… please insert submesh and try again. Action canceled.
If I click Create shell before clearing mask I get “Mask must be cleared in order to dynamesh”

What am I doing wrong?

[beta_channel]

hold ALT while putting your cylinder down so it is a negative (subtraction) mesh

[system]

Thank you very much! It was so simple!