Every model below is live and runs entirely in your browser. They stand in for the real subsystems to make each architectural decision tangible.
Drive a charge step by step and watch where the PAN is allowed to exist; try to tamper with the amount.
Charge, fee, payout, dispute-hold and refund; watch entries append and available balance recompute.
Fire a duplicate paid webhook and watch the compare-and-set absorb it as a no-op.
Plan rates and who-pays, run through the ordered fee pipeline with the customer gross-up.
Enter a code; the server resolves it (valid, product-scoped, expired, or invalid).
Watch the merchant_records join get injected, plus the skip_org_id and fail-open paths.