If ContractorTools tells you there is an update available, and you go to the App Store to install the update, but the button in the App Store does not say "Update", the reason is because the update for ContractorTools requires a newer version of the operating system (macOS on a Mac, or iOS on iPhone or iPad) than you currently have on your computer/device.
When this happens, you must first update the operating system before you can update ContractorTools.
To update the operating system on a Mac:
Click on the Apple icon in the upper left of the screen and select "About this Mac"
Then click on "Software Update..." in the Overview tab.
To update the operating system on an iPhone or iPad:
Go to Settings > General > Software Update
Note: When a Mac or iPhone/iPad reaches a certain age, it becomes no longer possible to update the operating system. Why?
Without going into too much detail, Apple computers are much more "machine efficient" than PC's and Android devices because Apple designs and manufactures both the hardware and the operating systems. This provides the opportunity to take advantage of significant efficiencies by synergy between the hardware and software that is not possible otherwise. A consequence of this is that the hardware and software have to be compatible in order to implement advances in one or the other.
To do that, sometimes it becomes necessary to require an upgrade to the hardware to maintain compatibility with the advancing operating system. When that happens, the only option is to purchase a new(er) version of the computer or iPhone/iPad.
Here is an article which shows which versions of the operating systems your Mac is compatible with: https://support.apple.com/en-us/HT201686
And here is an article which shows which versions of the operating systems your iPhone/iPad is compatible with: https://everyi.com/by-capability/maximum-supported-ios-version-for-ipod-iphone-ipad.html
So what happens if you don't upgrade your computer or device in order to update the operating system?
ContractorTools will not prevent you from running with different versions installed on each computer or device, but there are risks involved in doing that so we don't recommend it, and we cannot guarantee that you will not have problems.
Depending on what the differences are between the ContractorTools versions, it's possible that data will not sync between them correctly or it could become corrupted. It's also possible that the app will behave differently from one version to the next, and this could cause confusion.
If you only run ContractorTools on a single device (so you do not sync data between devices), you can continue to run an older version of ContractorTools on that device, but if you encounter problems that were fixed in later versions of ContractorTools, you will not be able to get those problems resolved without updating to the latest version.