code: func (api *API) ValidateFilterExpression(expression string) error {
  	uri := fmt.Sprintf("/filters/validate-expr")
  	expressionPayload := FilterValidateExpression{Expression: expression}
  
  	_, err := api.makeRequest("POST", uri, expressionPayload)
  	if err != nil {
  		var filterValidationResponse FilterValidateExpressionResponse
  
  		jsonErr := json.Unmarshal([]byte(err.Error()), &filterValidationResponse)
  		if jsonErr != nil {
  			return errors.Wrap(jsonErr, errUnmarshalError)
  		}
  
  		if filterValidationResponse.Success != true {
  			// Unsure why but the API returns `errors` as an array but it only
  			// ever shows the issue with one problem at a time ¯\_(ツ)_/¯
  			return errors.Errorf(filterValidationResponse.Errors[0].Message)
  		}
  	}
  
  	return nil
  }
docs: // ValidateFilterExpression checks correctness of a filter expression.
  //
  // API reference: https://developers.cloudflare.com/firewall/api/cf-filters/validation/