What state to pay state income tax on proceeds?

I am a developer residing in Pennsylvania. Do I pay state income tax to Pennsylvania or to California for my app proceeds? Typically, if I get paid by a company in California, I would need to pay state income tax to California. But Apple is not my employer, so I'm not sure.

I do not think it is relevant, but FYI I am not receiving a 1099 from Apple, since my proceeds are below the threshold for them sending 1099.

What state to pay state income tax on proceeds?
 
 
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