What operating system are you using, and which version number?
Are you using the latest version of the eBay app?
I seem to be able to search, open listings, and add items to my cart using version 6.116.0.1 of the eBay app on my Android phone.
Some app issues can be dealt with by uninstalling the eBay app, restarting your device, then installing the latest version of the app. The restart in between should ensure a clean install.
