We are a UK based company, but we are selling our software through FastSpring (Bright Market, LLC), our payment processor.
FastSpring (which is a US company) will be the vendor in the transaction and their company information will be on your invoice, so the vendor should be set up in their name and not ours.
Everything a vendor form asks for – addresses, remit-to details and tax IDs, along with their current W-9 – is on FastSpring’s supplier page.
If your form has a separate field for the software publisher, you can find such details on our contact page.