Request body for updating a collection's page: hero, about and overview. Top-level fields you leave out keep what is saved. Each field you send replaces what is saved for it, as its description says; overview in particular is replaced as a whole. Media fields take a token from POST /api/v2/collections/{slug}/media/{placement} or POST /api/v2/collections/{slug}/images/{image_type}. To keep media that is already saved, send its url from GET /api/v2/collections/{slug}/metadata as the token. Read the result back with GET /api/v2/collections/{slug}/metadata.