Check to see what browser is set on your device as the "default" browser. It may not necessarily be the browser you normally use.
The app may need to open a browser window to deliver some information the app is not designed to handle -- such as a disclaimer notice or an agreement you need to check a box to show you have read, or to open a PayPal sign-in page -- when that happens, the app will open your device's default browser. If the default browser is some obscure, proprietary browser, the app may not recognize it and it may give you that error.
If you change your default browser to a more popular browser such as Chrome or Firefox, that may avoid that error when you are using the eBay app.
