What version operating system are you using, and what version number of the eBay app?
Old versions of the app may not work correctly; make sure you are using the latest version for your operating system.
Try uninstalling the eBay app, restarting your device, and then installing the eBay app once more. The restart in between should ensure a clean install, if the problem was with a previous installation.
Otherwise, try using a browser to go to ebay.com instead.
