Error 400 while trying method customers.googleAds.search

Question

Description

The following Google Rest API interface allows to test the method using customerID and developer-token parameters: https://developers.google.com/google-ads/api/rest/reference/rest/v18/customers.googleAds/search

Below is the error message I received after inputting a customerID and developer-token:

{
  "error": {
    "code": 400,
    "message": "Request contains an invalid argument.",
    "status": "INVALID_ARGUMENT",
    "details": [
      {
        "@type": "type.googleapis.com/google.ads.googleads.v18.errors.GoogleAdsFailure",
        "errors": [
          {
            "errorCode": {
              "queryError": "UNEXPECTED_END_OF_QUERY"
            },
            "message": "Error in query: unexpected end of query."
          }
        ],
        "requestId": "pQ7QHjhX6BfdTpxkTRv2GQ"
      }
    ]
  }
}

Troubleshooting steps

I have used the following method to verify that the customerID and developer-token are valid: https://developers.google.com/google-ads/api/rest/reference/rest/v18/customers/listAccessibleCustomers

Question

It appears the customerID and developer-token are the only required parameters to test the API. Can someone recommend any additional configuration to include in this test in order to get around the error?

Thank you!