RE: Form 1042-s9 May 2024 01:03
Ok, thanks to Vistaman and Justanotherbat, I have a definitive answer to the question you asked about 1042-s.
It's for reference only, your broker was the issuer, and it shows details of payments received, and tax withheld. If you've filled in a W8-Ben with your broker, to reduce the tax withheld as a non-resident of the US, if applicable, on shares held in an ISA or SIPP. You must have some sort of exotic broker, if they're going to the trouble of issuing a 1042-s. But the parts - or copies - BCD are just for your reference in case you have to fill in a US tax return.