Cannot add permissions in IAM Identity Center

I am trying to follow the instructions in the guide in order to configure access through IAM Identity Center of an admin user. I have created the corresponding user and group as instructed, however in the part where I have to add administrative permissions, I cannot find the Multi-account permissions in the navigation pane. Could this be due to the fact that I cannot enable access to the IAM Identity Center enabled applications? As every time I try to enable it, I get an error saying:

Sharing feature is not supported for an account level instance with id ssoins-7223decfb79b7ca3