How much free space is on your iPad Air? To find out, open Settings ➡️ General ➡️ About ➡️ Available: Here, you will see how much space is actually available on your iPad Air.
You may have Offload Unused Apps set to ON in Settings ➡️ App Store ➡️ Offload Unused Apps. When this setting is ON, then your iPad Air will offload unused Apps to create space on your iPad Air when space is not available. The app gets downloaded when you are ready to use it. NOTE: The app data never gets offloaded.
I believe, what may be happening with your iPad Air is that there is very little free space available on it. Offloading unused apps is no longer effective and therefore you are unable to download the app(s) so that it can function properly on your iPad Air.
If space is nearly full on your iPad Air, then try deleting some data on your iPad. Media files take up the most space so begin with unwanted Videos, Photos and Music.
Axel F.