NoSuchDriverError Error on invoking mobile safari

HI,
I have been trying to automate the following:
Paste a URL in mobile safari which would invoke a ios app. This is required since the entry point(correct landing screen) for our app we are building/testing is from another app. We don’t want to bring such a dependency in our functional test suite. Hence, we have figured an api which is a URL that would invoke the second app(with the desired landing screen). When we would hit this URL in browser, then the app which we are testing is invoked.
Now, following is the desired capabilities used in the test:

platformName = “iOS”
deviceName = “iPad Simulator”
app = “safari”
browserName = “Safari”

The mobile safari is invoked but am getting following error: Selenium::WebDriver::Error::NoSuchDriverError.
The line of code wherein the error occurs is:

$atlas_auditor= Appium::Driver.new(caps).start_driver

In terms of appium logs I don’t see any error.

I am using ruby, appium_lib

Can someone help me on this?

Thanks,