Create a product in one of your MU stores. Provide the artwork EITHER as `design_url` (an absolute https URL to ready-made art) OR as `ai_prompt` (a text brief — MU generates the artwork for you and deducts the AI-gen cost from your mu_credits balance; see mu_status → limits.ai_gen for cost_jpy and whether it is enabled). Pass exactly one of the two. `kind` must be one of: tee, tee_white, rashguard_ls, rashguard_black, hoodie, crewneck, sticker, mug, tote, tank, cap, phone_case, long_sleeve_tee, shorts, beanie, leggings, joggers, apron, canvas, metal_print, pillow, blanket, coaster, placemat, journal, mug_black, wine_glass, towel, bottle, mouse_pad, laptop_sleeve, poster, nfc_coin, device, event_ticket, song, zine, video, karaoke_ticket, house, socks, drawstring_bag, beach_towel, fanny_pack, bucket_hat, kids_tee, backpack, flag, printful_custom. `phone_case` is an iPhone tough case (Printful) — the buyer picks their iPhone model (11〜17, all sizes) inside checkout, so you create ONE product and it ships to whichever model they choose. . Two digital kinds need an extra field: `event_ticket` (a sellable event ticket — pass `capacity` for the seat limit; on purchase the buyer is emailed a QR that opens a VALID ticket page; no shipping) and `song` (a sellable track — pass `audio_url`, the https link to the audio; on purchase the buyer is emailed a private listen/download link; no shipping). Other digital kinds (`zine` PDF, `video`, `karaoke_ticket`) and manual-fulfilment kinds (`poster`, `tee_white`, `nfc_coin`, `device`, `house`) all take the same `design_url`/`ai_prompt` artwork; the buyer gets a download/redemption link (digital) or the operator ships/builds it (manual). Products go live immediately for trusted owners unless the risk gate trips, otherwise they wait for MA-council review — ALWAYS report the `status` field from the response, do not assume. Requires `Authorization: Bearer <api_key>`.