Samsung stopped providing updates, including security patches, for the S9 series in April 2022
The S9 is running an older version of Android, and developers are less likely to support apps on older operating systems.
So it may well be the reason.
Edit
Quick Google search brought up this.
Yes, the latest versions of the eBay app no longer support devices running Android 9 and below, including the Galaxy S9. This is because eBay has updated the app to require Android 10 or higher. Users on older Android versions will need to update their phones or use the eBay website on a browser.
