Here we will cover why City-MP and FX cannot function together.
FX is the current build or iteration of FiveM, which came after City-MP/Citizen MP. Unlike its predecessor, FX has loads of performance updates and stability fixes. This is the reason why FiveM no longer supports City-MP or release any other updates for it.
In your Mod Manager, you will notice that we still offer the capability of installing City-MP mods, but do note that they do not mix well with an FX framework. This will lead to server issues such as being unable to launch the server properly.
An official discussion in the FiveM's forum can be found here for further reference: https://forum.fivem.net/t/deprecating-citizenmp-server/36810/67
