Hi there, craigjf 1, maybe I can help you.....
the reason you're getting that message is that Catalina has certain requirements. and/or, you're not signed up with the Apple Beta Program. The most current version of Catalina is 10.15.3.... and anything else is a beta. seeing as how you have a MacBook Pro, the requirements for that are one from Mid 2012 or newer. You can find out the date of manufacture by going to the large Apple Icon at the top left of your screen, then going to "About this Mac", which should give you a rough model number. Remember that number, and using your Web Browser, go to everymac.com, and type it in under the "Search" window, which will bring up the stats for that model of MacBook Pro. The official way to do it is to grab a copy of Catalina from the App Store. If it doesn't want to install right off the bat, you could try doing a reset smc/pmu and zap pram, then trying to install it. How to do the reset smc/pmu and zap pram can be found on Apple's support page for Notebooks, or if you know the model number, google or yahoo can help you out there, too...
There is an unofficial way, but I can't talk about it here.
good luck
John B