If you are a non-US company, you have nothing to file for the USA. Some European countries do not require any form pertaining to your collaboration with Sherpas in the USA, but we recommend that you check tax regulations pertaining to your home country, be it in Europe or on other continents.
If you are a US company (or have a US entity) and if you want Sherpas to bill you in the USA, don’t forget to ask them aW-9 form so that your accounting department can comply with US tax regulations. It applies to LLCs, LLPs, and freelancers or independent contractors.