Originally we had two paid versions of Quick Sale available on the App Store:
Quick Sale: Basic, upgradable to Pro with an in-app purchase
Quick Sale Pro: Stand-alone version, replaced by the new subscription version
The upgradable version was discontinued some time ago and it in no longer available on the App Store, but you can still download and update this version by following these steps:
Open the App Store app on your iPad, then tap Today at the bottom of the screen.
Tap the person icon or your photo in the upper-right hand corner, then tap Purchased
Search for "Quick Sale"
If Quick Sale appears in the results list, tap the download button
To restore the Pro upgrade (in-app purchase) please follow these steps:
Open Quick Sale (not the subscription version, both apps have the same icon)
Go to Settings
Tap Upgrade > Restore Previous Purchases
If you would like to move to the new subscription version, you can use the backup/restore feature to transfer your data.