Not able to locate element in iOS hyprid app(build in Ionic) automation using Appium on real device

I am trying to automate a hybrid app(developed using ionic framework) on iOS device. But I am not sure which locators to use. I an trying to access elements using ‘by.css’, but that gives error saying “Locator strategy : css selector is not valid for this session”. Please provide inputs to the same.

Configuration : Appium : 1.7.2 Protractor :5.3.0 Xcode : 9.2 iOS : 11.2.2 Device : iPhone 6+ MacOS : 10.12.6