Could you try webhook.site with both Postman and HTTP Request to visually check if there is any difference in what is being send out by both activities?
One suggestion would be to try sending the Cookie via the Cookies parameter of the HTTP Request activity, and splitting it per cookie name and value:
So there is still something wrong. I already tested that before as well. And sending via header is not correct I would say. It needs to be send via cookie paramter.