Mercari Shipping Label Problem Blame Is Put On Me

I sold a pricey item on Mercari like two weeks ago, sent it right away to the buyer using the label that was given to me, a few days earlier, got a message from carrier saying that the package had been seized because the postage was fake. sent an email to Mercari asking for an explanation and a solution, but I have not received a response. even scarier, when I looked into it more, found that other Mercari customers have recently had the same problems, which suggests that there may be a problem with how Mercari works as a whole, expected better service and more accountability. It is disappointing to see that customer concerns are not taken seriously and that problems are not being dealt with openly.