The same dataset has been defined more than once.

How to fix

Ensure that you have defined each dataset only once.

Problem example:

{
  "tables": [
    {
      "schema": "Person",
      "name": "Address",
      "columns": [
        {
          "name": "City",
          "dataset": "CustomCities",
          "deterministic": false
        }
      ],
      "datasets": [
        {
          "name": "CustomCities",
          "type": "List",
          "values": ["Seattle", "Portland", "Vancouver"]
        },
        {
          "name": "CustomCities",              // Duplicate dataset name
          "type": "Pattern",
          "values": ["????ville", "????ton"]
        }
      ]
    }
  ]
}

Ensure that you have defined each dataset only once:

{
  "tables": [
    {
      "schema": "Person",
      "name": "Address",
      "columns": [
        {
          "name": "City",
          "dataset": "CustomCities",
          "deterministic": false
        }
      ],
      "datasets": [
        {
          "name": "CustomCities",              // Single dataset definition
          "type": "List",
          "values": ["Seattle", "Portland", "Vancouver"]
        }
      ]
    }
  ]
}