Returns the same metadata as GetFileInfo for up to 50 files in one call, for example all the fileIds of a webhook.

Files you can read are returned in files, in request order. Every other requested ID is listed in notFound: IDs that do not exist, were deleted, are malformed, or belong to a fund or order the service account cannot access. Duplicate IDs are answered once.

The request is rejected with 400 when fileIds is empty or has more than 50 IDs.