There's only one officially authorized multiplayer modding platform for GTA, and it's not Rage:MP.
Take-Two Interactive, the parent company of Rockstar Games, has ordered the GTA 5 modding platform Rage: MP to cease operations.
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Take-Two issues cease-and-desist to GTA V modding platform

Take-Two Interactive issued a cease-and-desist to another modding platform. As Rockstar Games consolidates its multiplayer ...
Take-Two and Rockstar Games have shut down another mod service as GTA 5 multiplayer modding is solidified around the FiveM ...
RAGE Multiplayer is an alternative multiplayer modification for Grand Theft Auto V that allows you to play, host and create your own custom built game modes on Grand Theft Auto V using C++, C# and ...