When i try to buy a diamond chest it gives me the message: price does not match with server. I can however use diamonds on other stuff and i can buy the gold chest just fine
Is this on Steam, Android or iOS?
Regardless though, this is not a known problem any more. Maybe turn your phone off and back on, or reboot your computer if the Steam game?
There is a bug with buying the diamond chest:
https://forum.paradoxplaza.com/forum/index.php?threads/warning-bug-with-chest-purchases.1087385/
But that is not what you are saying. Have you tried it while inside a saved game?