Fetch TikTok slideshow metadata + image URLs before importing into an editable Genviral slideshow.
preview_id so the follow-up import call can skip re-fetching upstream TikTok data.
slide_count is the number of slides that will be imported (max 8).
If TikTok has more slides, capped=true and total_slides shows the original count.400 invalid_json - request body is not valid JSON422 invalid_payload - payload is missing required fields422 invalid_tiktok_url - URL is not a valid TikTok link422 not_slideshow - TikTok URL is valid but not a slideshow/photo post429 rate_limited502 tiktok_fetch_failed - upstream TikTok fetch failed500 upstream_config_error - TikTok upstream credentials/config missing500 preview_failed