enable experimental features on an existing server

as the title. I guess its not a datapack in the traditional sense, but i dont know where else i would seek help. I needto enable it using the NBT data in level.dat, i know, but i add enabled features, and move the datapack from disabled to enabled, yet nothing... It says i cant enable it because
Pack 'minecart_improvements' cannot be enabled, since required flags are not enabled in this world: minecraft:minecart_improvements!