Reboot your game.
If that does not work, restart your computer.
If both of these suggestions to do not work, send a report in and go play another game.
What an absolutely condescending rubbish and ridiculous response. He bought this game, he expects for it to function and it barely does. The market is complete trash, hate to say it as I was always on-board with an online integration system but at this point I wish it was just gone or optional. I'd much rather research animals before being able to unlock and buying them, and then do trading with other players or just keep rolling the dice with the RNG offline zoos.
The interface and the entire system is borderline unusable. In order to buy an animal you have to click things over and over until it decides to work, pressing 'buy' on the perfect animal (by which I mean stats because that's all they are: numbers) and getting an error message since someone else got it while you spam clicked the button feels beyond terrible, even moving animals into enclosures, trading them, releasing them feels like a pain because of the AWFUL INTERFACE.
I've played many games, like a lot of them. And without a doubt, this is one of the cases I can say this game has an integral part of its systems completely broken, unusable and unstable. The market sucks, Frontier.