Assuming paymentInstrument is the name of the json file, try this
.body(ElFileBody("**paymentInstrument**.json")).asJSON
Assuming paymentInstrument is the name of the json file, try this
.body(ElFileBody("**paymentInstrument**.json")).asJSON
Can you share how are you define the paymentInstrument var?
Correction: Can you share how paymentInstrument was defined?