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.

RT is not bannd, but sanctioned due to being fully owned by the Russian government. The content they produce is not illegal, but US companies are not allowed to work with them. Stripe just wants to avoid problems and bsas them, due to Blinken claiming they are connected. That does not have to be true, but it pretty much gurantees legal trouble for Stripe, if they keep them as clients.

But also they are clearly professionals. Most employees having worked for Russian, Chinese, Iranian or Venezuelan state media is a clear sign. It also makes a direct connection to RT much more likely. So I get why Stripe wants to get far away from this.