"code": "RefundLinesRequired",
	"target": "Unknown",
	"details": [
			"code": "RefundLinesRequired",
			"number": 704,
			"message": "For Partial refund, refund lines cannot be null",
			"description": "For refund type -0-, refund lines should be specified",
			"faultCode": "Client",
			"helpLink": "",
			"severity": "Error"

The RefundTransaction API allows you to specify the type of refund. You can refund an entire transaction, a partial transaction, or a percentage based refund. If you specify a partial refund, you are required to specify the lines that are being refunded.

This error message occurs when you specify refundType = Partial on your RefundTransactionModel, but refundLines = null. To fix this error, set the refundLines parameter to a non-null value.