The Rocket League Version Mismatch Issue alway happened after a big update. there are lots of players will report this mismatch error when the new update released. the latest update 1.51 has released recently, although the Rocket League 1.51 Update brings forth hotfixes that will affest gameplay. which will optimize the game better.
The Version Mismatch still happened for a match saying”Version mismatch. Please get the latest version of the game.”. Here RocketLeagueGuide will give you the valid way to solve the Version Mismatch issue:
Download and install the most recent Rocket League update.
However, the question is that the Steam won’t update the game automatically? the Steam will download the new update automatically if you have the game set to priority.