Mask Paint Duration

Hello, I am currently trying to use a mask paint to mask off areas that a luma key has flaws in. The mask is working, however it is only applying it to one frame. I ran the Stroke Duration up to 30, however it does not last the duration of the timeline. In the manual, it says that "Each stroke can have a duration that lasts for the entire project, a single frame or field, or an arbitrary number of fields."

How can I set the mask so that it lasts the entire project as opposed to only one frame?

Thank you

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