$resp = $this->instance

      ->chain('v3/refund/domestic/refunds')

       ->post(['json' => [

                'transaction_id' => $transaction_id,

                'out_refund_no' => $out_refund_no,

                'reason' => $refund_reason,

                'notify_url'   => Yii::$app->params['pay_notice'],

                'amount'       => [

                    'refund'   => $refund_fee,

                    'total'    => $total_fee,

                    'currency' => 'CNY'

                ],

                'funds_account' => 'OPERATION'

            ]]);

Client error: `POST https://api.mch.weixin.qq.com/v3/refund/domestic/refunds` resulted in a `400 Bad Request` response: {"code":"PARAM_ERROR","detail":{"location":"body","value":"OPERATION"},"message":"无法将 JSON 输入源“/body/funds (truncated...) 400 Bad Request {"code":"PARAM_ERROR","detail":{"location":"body","value":"OPERATION"},"message":"无法将 JSON 输入源“/body/funds_account”映射到目标字段“退款资金来源”中，此字段需要能映射到一个合法的“/body/funds_account”枚举"}