Google have a nasty habit of not allowing Android to be backwards compatible for long.
For example: I have been running Wiki Camps quite happily on my expensive and high end Asus tablet for about three or four years. This tablet runs Android 4.
Recently I performed a "factory reset" on the tablet and subsequently went to the Play Store to reload my apps. To my surprise Wiki Camps was not available to me as the newest release of it requires Android 5 or higher and there is no facility to download an earlier version.
That's it - you're stuffed. Go out spend a few hundred dollars on a new tablet even though your existing device is working well and to your satisfaction.
Unless... you have been around computers as long as me and don't trust the bastards or OS producers as far as you can throw them.
Fortunately when I first started using Android I also downloaded this:
It is a tool which extracts all required parts of an existing installed app. and stores them as an "apk" file - this is a file type which can be installed to Android - in other words it backs-up your apps. and I strongly suggest you download it and use it for all important apps then store them on a PC or USB stick.
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"I beseech you in the bowels of Christ think it possible you may be mistaken"
Oliver Cromwell, 3rd August 1650 - in a letter to the General Assembly of the Kirk of Scotland
Hi Mike, I downloaded the APK Extractor and when I tried to move the app I was told "Cannot extract, storage permission denied", any idea why this would be so, I have average skills but still don't understand a lot, cheers Paul.
The issue with running older versions of software that rely on a server for data, is you can't really ever backup correctly. The WC database is ever-changing and doesn't live on your device. The data stored on you device is only as good as the last time you backup after a successful connection. What works today, may not work tomorrow.
Another issue is the likelihood that WC servers will stop recognising older versions. Given one change made is based around served and database security, that may happen anytime. It costs money to support older apps and that's why only the very largest of companies even consider it a long term prospect.
It pays to upgrade sooner rather than later.
However, unlike Apple who legally control all technical iOS development, Google and device manufacturers only control newer Android releases. Once released, it's legally anyone's to play with and change. There are large groups of technical junkies developing upgrades and variations to existing Android versions and devices to prolong their lifetimes. Do a web search and you might find your device has free third party upgrade. They usually have detailed step-by-step how-to instructions. Read them thoroughly plus and caveats.
There are also libraries of older versions of software. There is at least one that has all previous versions of Wikicamps. You will need to have enabled "APK installation" and/or "install from unknown source"