Do I have to register my LLC in the states where I sell?

Not usually for online sales from abroad. You register in another state when you do business there, for example with staff, an office or stock in a warehouse. Registering a foreign LLC costs US$200 in Delaware as of September 2026, and every other state, Wyoming included, sets its own fee and its own test for doing business.

Source: Fee schedule (revised 1 August 2026), Delaware Division of Corporations