Search Keywords throwing Error 500 with INVALID_VALUE_FORMAT

[NecoHorne]

Running the API with multiple keywords throws an error 500 even with the test/demo call from the documentation IE:
http://api.mediastack.com/v1/news?access_key=<API_KEY>&keywords=virus,-corona

Yes API key hidden in the above example.

Response from the API:

{
  "error": {
    "code": "validation_error",
    "message": "Validation error",
    "context": {
      "keywords": [
        "INVALID_VALUE_FORMAT"
      ]
    }
  }
}