Make sure you have the latest version of the eBay app for your particular operating system. For Android devices get the latest version from the Google Play Store; for iOS devices, try the App Store app.
For more specific details of using the eBay app, try posting your question on one of the eBay app boards. Be sure to mention the device model and operating system version you are using:
https://community.ebay.com/t5/Mobile-App-Android/bd-p/androidapp
https://community.ebay.com/t5/Mobile-App-iOS/bd-p/iosapp
If your operating system is too old to use the latest eBay app, you should still be able to reach ebay.com using a browser on your device.
