Anyway Create Checkout

Build the Anyway checkout URL for a buyer-customizable-amount product.

The single payment link accepts any amount within [ANYWAY_MIN, ANYWAY_MAX]; buyer attribution (user_id + a unique merchant_reference) and an amount pre-fill hint ride along as query parameters. The signed order.paid webhook — not this URL — is the fulfillment signal and credits the amount actually paid, so query params are buyer-visible correlation data only.