@SlaviSavanovic
1. When you upload files via the API and reference them later, you should select 'Custom' as the knowledge base source if you are referring to files that are specific to your application or use case. 'Canonical' is typically used for pre-existing or standard knowledge bases provided by the API.
2. 'Canonical' does not specifically refer to VAPI uploads. It usually refers to a standard set of knowledge that the API might have built-in, which is universally applicable and not specific to any single user or organization.
3. The structure you've provided seems to be for a different API. For VAPI, to include file IDs in API calls, you would typically use the file ID in the endpoint or the body of the request where the file is being referenced. The exact structure would depend on the specific API call you're making. If you need to reference a file by its ID, you would use the 'id' field provided in the context. If you can provide more details on the API call you're trying to make, I can give you a more precise answer.