PaymentRequestEvent.instrumentKey - Web APIs
the instrumentkey read-only property of the paymentrequestevent interface returns a paymentinstrument object reflecting the payment instrument selected by the user or an empty string if the user has not registered or chosen a payment instrument.
... syntax var instrumentkey = paymentrequestevent.instrumentkey value a paymentinstrument object.

Index - Web APIs
2944 paymentrequestevent.instrumentkey the instrumentkey read-only property of the paymentrequestevent interface returns a paymentinstrument object reflecting the payment instrument selected by the user or an empty string if the user has not registered or chosen a payment instrument.

PaymentRequestEvent() - Web APIs
options optional options are as follows: instrumentkey: a paymentinstrument object reflecting the payment instrument selected by the user or an empty string if the user has not registered or chosen a payment instrument.

PaymentRequestEvent - Web APIs
properties instrumentkeyread only returns a paymentinstrument object reflecting the payment instrument selected by the user or an empty string if the user has not registered or chosen a payment instrument.