help iam new to json

[scotty533]

can somebody tell me how to create this please {
  "SubscriptionId": "7620A519",   "MainData": [     {
      "TransactionAgreement": {         "TransactionSource": {
          "Institution": "Test Bank",
          "AccountHolder": "John Doe",
        },
        "Reference": "EXT-AAA-0000001"
      },
      "TransactionsToSchedule": [
        {
          "ScheduledDate": "2021-03-11T00:00:00+10:00",           "Reference": "AAAAA-BBB-CCCCC-DDD-EEEEE"
        }
      ]     }
  ] }