I'm a NON US resident but I have a SSN and I formed an LLC in Wyoming. Do I have to apply for EIN or I can use my SSN? I am the only member of an LLC.
You need to register for an EIN from the IRS before you start cutting paychecks and withholding taxes for your employees. In the US there is a layer of Federal requirements on top of the state-level requirements, and this is one of those cases: there’s not going to be a Wyoming-specific EIN but instead an EIN from the IRS. See irs.gov for the online form.