how to process data that are transmitted as a string, but in fact are an array?

there is a task to make a service that takes on the input string via POST, and process it. the problem is that the string is actually an array, and I can’t figure out how to process it correctly. I couldn’t split it with explode(), because neither the comma nor the arrow separators fit – everything spoils the second key-value pair, where the value is a JSON string. Is there any way to process it? Below is exact incoming string

'Number' => '0000-543392',
  'In' => '
    {
      "RequestID": 8101,
      "DateTime": "2023-10-26 16:47:49",
      "CheckNumber": "0000-543392",
      "DateTimeCheck": "2023-10-26 16:47:44",
      "ChannelID": 2,
      "SourceID": 1,
      "CashDeskID": "c6445ae8-dce2-11e8-80cf-0050560132c4",
      "Coupon": false,
      "CouponCodes": null,
      "CustomerIdentifier": [
        {
          "CardID": null,
          "CustomerID": null,
          "CustomerPhone": null,
          "TelegramID": null,
          "CustomerEmail": null
        }
      ],
      "StringAmount": 2,
      "Strings": [
        {
          "ProductID": "56625578-a627-11ed-97b9-00155d05fc14",
          "UUID": "56625578-a627-11ed-97b9-00155d05fc14",
          "ProductPrice": 28,
          "ProductAmount": 1,
          "BasePriceID": null,
          "Sum": 28,
          "ExpirationDate": [
            {
              "Amount": null,
              "ExpirationDate": null
            }
          ],
          "TypeLabel_ID": "",
          "DataMatrix": []
        },
        {
          "ProductID": "9b86934c-3f30-11ed-97b9-00155d05fc14",
          "UUID": "9b86934c-3f30-11ed-97b9-00155d05fc14",
          "ProductPrice": 45,
          "ProductAmount": 1,
          "BasePriceID": null,
          "Sum": 45,
          "ExpirationDate": [
            {
              "Amount": null,
              "ExpirationDate": null
            }
          ],
          "TypeLabel_ID": "",
          "DataMatrix": []
        }
      ],
      "CheckSum": 73,
      "PaymentType": [
        {
          "PaymentTypeID": 1,
          "CurrencyID": 3,
          "CurrencyName": "Rub",
          "Sum": 0
        }
      ],
      "WriteOffBonusType": 3
    }
  ',
  'success' => 'false',
  'DateTime' => '26-10-23 16:47',
  'RequestID' => '71457',
  'reqlenght' => 'null',
  'timestart' => 'null',
  'timeend' => 'null'

explode didnt help…