Hi howard53,
When 403, it’s because you are not authenticated from within the API. Your endpoint is related to editing a post, so meaning you need to have authenticated for the right to edit the post before reaching this.
Meanwhile, you also need to know that even if you logged in admin panel, you’re still considered unauthenticated in the REST API request, as you need to set some kind of token or authentication header in each request as per WordPress specification.
You might want to look that up here:
If you’re developing an application, you might also want to know about the security feature here on InfinityFree, which might be in your way if you attempt curl elsewhere, or outside of your existing session to the server.
Cheers!