Publishing error. An error occurred while publishing. Portal creation failed. Please try again later.

Are portals enabled on your account?  FYI the service costs extra, over and above the normal Appian Cloud hosting costs, and this is the exact error message I get (for instance) when I try to publish one in my environment where we do not have them enabled.  (Note: you didn't specify whether you're referring to a Community Edition instance, which does have portals, or a regular cloud instance, etc, so I'm assuming it might be the latter.)

Are portals enabled on your account?  FYI the service costs extra, over and above the normal Appian Cloud hosting costs, and this is the exact error message I get (for instance) when I try to publish one in my environment where we do not have them enabled.  (Note: you didn't specify whether you're referring to a Community Edition instance, which does have portals, or a regular cloud instance, etc, so I'm assuming it might be the latter.)