I’ll try to outline, as simply as possible, what is going on - and how you may be able to resolve the issue. To save asking many questions, I’ll try to be as comprehensive as possible. It may sound complicated, but if you work through what follows, all should become clear. You will be able to identify key items that will influence your direction - and if possible, you will either be able to resolve the problem; if unable to resolve the problem, you will know why.
iOS (iPadOS) is the Operating System that runs on your iPad. Apps that are installed on your iPad, such as eBay, often have specific requirements (or use explicit elements of the Operating System) to function.
Both the Operating System and installed Apps are updated over time by the respective Developers - either to fix security issues, or to introduce new features. Very often, an update of the Operating System will require an update to one or more Apps.
Retuning to your specific issue…
The currently available eBay App requires your iPad to be running iOS 13.2 (iPadOS 13.2) or later. The current version of iPadOS is iPadOS 14.7.
The problem that you have is whether or not your iPad is capable of being updated to the current version of iPadOS. The tags that are associated with your post, indicating your iPad model, suggest that you have an iPad Air3. If this is the case, then you should be able to first update your iPad - and then install the eBay App.
However, the issue that you describe may suggest otherwise - with your iPad only having iOS 12.x (or earlier) installed. In this case you may have difficulties - as the iPad may not be an iPad Air3, but instead an earlier model which not be capable of update.
Whether or not you are able to update your iPad to a newer version of iOS/iPadOS will be dictated by your iPad model - and the currently installed version of iOS. You can find this information here:
Settings > General > About
Not sure which iPad you have? Identify your iPad model.
Here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:
iPad1 - iOS 5.1.1
iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)
iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)
iPad Air1, iPad mini2 and iPad mini3 - iOS 12.5.4
Newer models, not appearing in this list, are all able to be updated to the current version, iPadOS 14.7
If your iPad is capable of being updated to a more recent version of iOS/iPadOS than is currently installed, these support pages outline both the available methods by which the update can be performed - and troubleshooting should you experience difficulties:
Update your iPhone, iPad or iPod touch – Apple Support
If you can't update or restore your iPhone, iPad or iPod touch – Apple Support
If your iPhone, iPad or iPod touch won’t update - Apple Support
iOS update and restore errors – Apple Support
Be aware that your iPad may be too far behind the current version to be updated directly from iPad settings. As such, you will likely need to use a computer to perform the update. You will need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). Ensure that your installed version of iTunes has been updated to the most recent version; the essential device drivers are included.
Download and use iTunes for Windows – Apple Support
Update to the latest version of iTunes – Apple Support
Update software on iPhone, iPad or iPod touch in iTunes on PC - Apple Support
You should note that for your iPad to install an available update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - or be updated by a PC or Mac using iTunes or Finder - over a USB connection.
If you need more explanation, please don’t hesitate to ask.
