It is my understanding the Illinois is to source tax calculation at the origin address, and my transaction is not.
While Intrastate transactions (Illinois to Illinois) DO source and tax at the origin address, an interstate transaction will never calculate at the origin.
Interstate transactions will calculate at the destination address.
Note: Interstate transactions are taxed at the state-level rate; local jurisdidiction sales tax rates do not apply.
Customer did not realize the ship from was out of Illinois state.