Create a cashier payment order. Amount is in yuan and merchant_order_no is the merchant's own unique order number. After success, display pay_qrcode_markdown, the returned image content block, pay_qrcode_image data URL, or pay_qrcode_base64 with pay_qrcode_mime_type as the QR code. If QR rendering fails, show pay_url/qrcode as the fallback payment link. Save order_no/query_order_no when present. If order_no is null, save merchant_order_no plus order_time and use both for query_payment_order polling.

Query payment order status. Prefer platform order_no/orderid when create_payment_order returned it. If order_no is null, pass merchant_order_no plus order_time returned by create_payment_order. Pass either order_no or the merchant pair.

Create a refund request by platform order_no/orderid. mch_refund_no is the merchant refund number and must be unique per refund. Successful submission means accepted/processing, not final refund success; call query_refund_status to confirm.

Query refund status by platform order_no/orderid. Pass mch_refund_no when available to locate a specific partial refund. Only REFUNDED is final success; REFUNDING/PROCESSING means query again later.