Swagger Codegen OneOf

(Copying my answer from Stack Overflow)

The issue is probably that the InsuranceInfo schema

"InsuranceInfo": {
  "description": "Information about the payer, plan, and members.",

  "additionalProperties": false,
  "oneOf": [
    { ... },
    { ... }
  ]
}

effectively disallows ALL properties. This is because additionalProperties: false only knows about the properties defined directly alongside it and has no visibility into oneOf subschemas.

To resolve the issue, you can rewrite the InsuranceInfo schema without oneOf, as follows. This schema is basically "Option 2" from the original schema, except the dependentMemberInfo property is defined as optional.

"InsuranceInfo": {
  "description": "Information about the payer, plan, and members.",
  "additionalProperties": false,
  "type": "object",
  "required": [
    "payer",
    "policyHolderInfo"
  ],
  "properties": {
    "payer": {
      "$ref": "#/components/schemas/Payer"
    },
    "dependentMemberInfo": {
      "$ref": "#/components/schemas/DependentMemberInfo"
    },
    "policyHolderInfo": {
      "$ref": "#/components/schemas/PolicyHolderInfo"
    }
  }
}