isReadyToPayRequest returns false when I set the existingPaymentMethodRequired as true

I was following the instructions here to determine readiness for the Google Pay wallet. https://developers.google.com/pay/api/android/guides/tutorial#isreadytopay

This works fine until I set true to existingPaymentMethodRequired. My intention is to know if the wallet has at least one card, but I always get false from the request. My environment is test environment and the android phone has a credit card registered. Does anyone know why? The documentation is here https://developers.google.com/pay/api/android/reference/request-objects#IsReadyToPayRequest

public static Optional<JSONObject> getIsReadyToPayRequest() {
    try {
      JSONObject isReadyToPayRequest = getBaseRequest();
      isReadyToPayRequest.put(
          "allowedPaymentMethods", new JSONArray().put(getBaseCardPaymentMethod()));
      isReadyToPayRequest.put("existingPaymentMethodRequired", true);

      return Optional.of(isReadyToPayRequest);

    } catch (JSONException e) {
      return Optional.empty();
    }
  }

 private static JSONObject getCardPaymentMethod() throws JSONException {
    JSONObject cardPaymentMethod = getBaseCardPaymentMethod();
    cardPaymentMethod.put("tokenizationSpecification", getGatewayTokenizationSpecification());

    return cardPaymentMethod;
  }

private static JSONObject getBaseCardPaymentMethod() throws JSONException {
    JSONObject cardPaymentMethod = new JSONObject();
    cardPaymentMethod.put("type", "CARD");

    JSONObject parameters = new JSONObject();
    parameters.put("allowedAuthMethods", getAllowedCardAuthMethods());
    parameters.put("allowedCardNetworks", getAllowedCardNetworks());
    // Optionally, you can add billing address/phone number associated with a CARD payment method.
    parameters.put("billingAddressRequired", true);

    JSONObject billingAddressParameters = new JSONObject();
    billingAddressParameters.put("format", "FULL");

    parameters.put("billingAddressParameters", billingAddressParameters);

    cardPaymentMethod.put("parameters", parameters);

    return cardPaymentMethod;
  }

private static JSONArray getAllowedCardAuthMethods() {
  return new JSONArray()
      .put("PAN_ONLY")
      .put("CRYPTOGRAM_3DS");
}
private static JSONArray getAllowedCardNetworks() {
  return new JSONArray()
      .put("AMEX")
      .put("DISCOVER")
      .put("INTERAC")
      .put("JCB")
      .put("MASTERCARD")
      .put("VISA");
}
  private static JSONObject getBaseRequest() throws JSONException {
    return new JSONObject().put("apiVersion", 2).put("apiVersionMinor", 0);
  }


private void possiblyShowGooglePayButton() {

    final Optional<JSONObject> isReadyToPayJson = PaymentsUtil.getIsReadyToPayRequest();
    if (!isReadyToPayJson.isPresent()) {
      return;
    }

    // The call to isReadyToPay is asynchronous and returns a Task. We need to provide an
    // OnCompleteListener to be triggered when the result of the call is known.
    IsReadyToPayRequest request = IsReadyToPayRequest.fromJson(isReadyToPayJson.get().toString());
    Task<Boolean> task = paymentsClient.isReadyToPay(request);
    task.addOnCompleteListener(this,
        new OnCompleteListener<Boolean>() {
          @Override
          public void onComplete(@NonNull Task<Boolean> task) {
            if (task.isSuccessful()) {
              setGooglePayAvailable(task.getResult());
            } else {
              Log.w("isReadyToPay failed", task.getException());
            }
          }
        });
  }