- Add resolve_page_config() to determine PageConfig from cart/calendar context - Set page_config_id on Order during checkout - Pass page_config to SumUp create_checkout and build_sumup_reference - check_sumup_status uses order.page_config for per-page credential resolution - Fix: use session.flush() instead of g.s.flush() in check_sumup_status Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>