The same column has been defined in a table more than once.

How to fix

Ensure that you have defined each column only once.

Problem example:

{
  "tables": [
    {
      "schema": "Person",
      "name": "Address",
      "columns": [
        {
          "name": "FirstName",
          "dataset": "GivenNames"
        },
        {
          "name": "FirstName",          // Duplicate column name
          "dataset": "FirstNames"
        }
      ]
    }
  ]
}

Ensure that you have defined each column only once:

{
  "tables": [
    {
      "schema": "Person",
      "name": "Address",
      "columns": [
        {
          "name": "FirstName",          // Single definition
          "dataset": "GivenNames"
        }
      ]
    }
  ]
}