可以给讲解下loan_order_ext->"$.loan_pay_amount"这个语句是什么意思吗？

loan_order_ext为下图字段，loan_pay_amount是它其中一个子字段
loan_order_ext={"loan_order_id": "40546181", "order_start_at": "2021-07-24 23:22:53", "recommend_info": [{"amount": 300000, "periods": 12, "expireTime": 1629732172, "loanOrderId": 0, "periodsType": 2, "productType": 16}], "loan_pay_amount": "2000.00", "sale_loan_amount": "2000.00", "loan_order_ids_type": [{"loan_type": 1, "is_recommend": 0, "business_type": "1", "loan_order_id": 242223140940546181}], "task_over_order_status": "111"}