Enable root URL for FHIR server to save Bundle transactions?

My team is building a health app and thus using FHIR server. We need to save a bundle consisting of Condition, Observation and Procedure. The bundle should create each individual object in their respective tables. But when we are using postman to hit the base URL with a very simple bundle object it is giving Invalid URL. Each service is individually working fine and able to create respective objects. How can we enable the root URL of this FHIR server?

POST URL: http://localhost:3000/4_0_0/

POST Object:

{
  "resourceType": "Bundle",
  "id": "f001",
  "type": "transaction",
  "entry": [
    {
      "resource": {
        "resourceType": "Observation",
        "status": "registered"
      },
      "request": {
        "method": "POST",
        "url": "Observation"
      }
    },
    {
      "resource": {
        "resourceType": "Condition",
        "code": {
          "coding": {
            "system": "http://hl7.org/fhir/ValueSet/condition-code",
            "code": "",
            "display": ""
          }
        }
      },
      "request": {
        "method": "POST",
        "url": "Condition"
      }
    }
  ]
}

ERROR:

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "not-found",
      "details": {
        "text": "Invalid url: /4_0_0/"
      }
    }
  ]
}
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