im trying store some data that generated from WSS(WebSocketSecure) into JSON file

Forge MDK have common TOML config with using ForgeConfigSpec. in otherside, i wanna create JSON file with using ForgeConfigSpec. i take a look into External Libraries, Forge had use com.electronwill.night-config:toml:3.6.4  & com.electronwill.night-config:core:3.6.4 and unfortunately... i think ForgeConfigSpec only support TOML. but i've been implement com.electronwill.night-config:json:3.6.7 and now i dont have idea how to write ForgeConfigSpec as JSON file, does anyone know about that? please help me figure out how to write it

this is what i've been do since i think ForgeConfigSpec can't handle JSON file

@SubscribeEvent
static void onLoad(final ModConfigEvent event) {
    LOGGER.info(PREFIX);
    LOGGER.info(PREFIX+"Generating config");
    FileConfig config = FileConfig.of(CONFIG_FILE);
    config.set("pobab", "5000");
    config.save();
    config.close();
    LOGGER.info(PREFIX+"successful generated");
    LOGGER.info(PREFIX);
}

but, it said

[07:44:51] [main/ERROR] [ne.mi.fm.ja.FMLModContainer/]: Exception caught during firing event: No suitable format for forgeria-data.json

here is the full log