You can use the ID for a folder (or file) to retrieve the metadata for the item using /2/files/get_metadata, by passing in the 'id' string in the "path" parameter. Here's a simple example of that, first getting the metadata by path, and then by ID:
There are a few reasons you may get a 'path/not_found' error when attempting to do so though. For example, the ID may be for an item that no longer exists, or you may be using an access token for an account that does not contain the item identified by the ID.
Another possibility is that you're not using the right "root" for the item. The API call needs to be rooted in the correct "namespace" that contains the item in order to find it. By default, API calls are rooted in the user's own folder, so if the item isn't in the user's own folder, and is, say, in the "team space" instead, you'd need to configure the API call accordingly. I recommend reviewing the Namespace Guide for information on how that works.
Here's an example of that, of where a folder is in the team space, so trying to access it by ID without specifying the team space as the root fails:
We love to learn from the educators who use Dropbox. Whether you teach kids, teens, adults or a combination of all three, we want to know what apps and integrations you use with Dropbox to help with teaching. Which of the ones below is your favorite, or most used tool?