I think they are very similar but not compatible. Never tried it myself though, but bought a "real" HP printer when my Samsung went belly up and I couldn't really figure out if I would be able to use my still in stock Samsung toner on the HP178. Good luck!
The best thing is to contact the support team with the voucher code, they will certainly be able to help you. There is even a live chat at the bottom left of the page during office hours.
The toner cartridge "Clt-K404s (BK)" is compatible for Samsung printers of the Xpress series, including models such as SL-C430W, SL-C480, SL-C480FN, SL-C480FW, SL-C480W and SL-C483W. It is therefore also suitable for a Samsung C48x printer, as these models are included in the list of compatible printers.
However, it is important to note that the manufacturer's reference to "HP Inc." may be an oversight, as the toner cartridge was developed specifically for Samsung printers.