Stripe is a company that operates within the US and are subject to US law. The US passed a law that says that RT is subject to comprehensive sanctions. That means that it is now a criminal offense for any US company or person to do business with them. So Stripe doesn't have much choice and has to immediately stop doing business with RT. In the actual announcement, African Stream is called out by name. No proof needed because they are explicitly added to the list of sanctioned entities, and can enjoy being cut out of doing business with any company with a US or EU connection, just like ISIS, Boko Haram, and the PFLP.