Create simulation configuration for possible custom payment option.

Note: EXTERNAL engine plans cannot be fully configured at creation time — calculation_url is not accepted during creation. Create the config with PISMO plans first, then use the PUT endpoint to add or update EXTERNAL engine plans with their calculation_url.

{
  "config_id": "47589-uuye7-84k9",
  "description": "This is my simulation configurations",
  "plans": [
    {
      "id": "customId1",
      "description": "Electronics"
    },
    {
      "id": "customId2",
      "description": "Furniture"
    }
  ]
}