Hiccups are common when a game goes through a major change, and going free-to-play certainly counts. Epic Games and developer Psyonix had to contend with server issues as Rocket League player counts skyrocketed, but the issue affecting users this morning has been resolved, according to Epic Games' devs.
The game has received a surge of interest this month, and this may be one of those situations where Epic Games' servers just weren't ready for the unexpectedly large incoming population. According to the EOS Status feed, as of 12 PM PST (7 AM UTC) the issue has been resolved and players who may have been receiving errors such as "Call limit reached, try again later" can try to log in again now.
As of 11 AM 9/22 PST (6 AM 9/23 UTC), Downdetector reported over 3000 users saying they are having problems logging in, over twice the number of reports compared to a previous outing on the 16th, shortly after the announcement was made. This is likely due to the fact that as Rocket League goes free-to-play, more users are attempting to log in and join their multiplayer games than ever before.
Rocket League was the first Xbox One game to cross-play with PC, and it seems Epic Games has its hands full handling traffic from multiple platforms at once. The outage has been resolved for now, but there is always the possibility that another surge in players trying to connect to the servers could knock them out again. No game or company is immune from the effects of unusually large traffic spikes, simply because there is a hard limit on what the available servers can handle.
There is a catch besides the sudden surge in server demands and player counts in Rocket League's move to go free to play. For one, the change involved removing the game from platforms other than the Epic Games Store and consoles. This is a move the company may have felt necessary to ensure cross-platform consistency. It does appear that those who have already purchased the game through other means can still access the game.
Five years ago Rocket League surpassed 1 million sales on Steam, and it seems the game is still available to those who have already purchased it. Even though it's no longer available for purchase via Steam, the platform showed around 120 thousand concurrent players as of September 23rd. That is single-player, not multiplayer stats.
Rocket League is available now on PC, PS4, Switch, and Xbox One.
Source: Downdetector, SteamDB