The Configurable Interface

Unlike in spigot, in Hytale PAPI does not forward through Hytale's configuration API and instead implements its own. Effectively you'll be required to create a class representing your configuration section in PlaceholderAPI's main config.yml, and PAPI will handle the rest.

Create Your Config Class

CoolExpansionConfig.java

public final class CoolExpansionConfig {
    private String test;
    private String dateFormat;

    public CoolExpansionConfig(String test, String dateFormat) {
        this.test = test;
        this.dateFormat = dateFormat;
    }

    public String test() {
        return test;
    }

    public String dateFormat() {
        return dateFormat;
    }
}

Your config class needs to represent your config structure exactly. The only difference is in naming, in the above example, dateFormat will be converted to snake case (date_format) when reading the yaml. The above class will look like this in PAPI's config:

HelpChat_PlaceholderAPI/config.yml

expansions:
    coolexpansion:
        test: wew
        date_format: "dd/mm/yyyy"

Using Your Config Class

Once created, we need to tell PAPI about it. In your PlaceholderExpansion class, implement Configurable<CoolExpansionConfig>, you'll then need to also implement the 2 required methods.

CoolExpansion.java

public final class CoolExpansion extends PlaceholderExpansion implements Configurable<CoolExpansionConfig> {
    @Override
    public Class<CoolExpansionConfig> provideConfigType() {
        return CoolExpansionConfig.class;
    }

    @Override
    public CoolExpansionConfig provideDefault() {
        return new CoolExpansionConfig("wew", "dd/mm/yyyy");
    }

    @Override
    public String onPlaceholderRequest(PlayerRef player, String params) {
        final CoolExpansionConfig config = getExpansionConfig(CoolExpansion.class);

        return switch(params) {
            case "test" -> config.test();
            case "date_format" -> config.dateFormat();
            default -> null;
        };
    }
}

That's pretty much it. PAPI will generate the default yaml from the values you provide in provideDefault() and write it to the PAPI config, then whenever your expansion starts it'll read the values from the config and put them into a CoolExpansionConfig object accessible via PlaceholderExpansion<T>.getExpansionConfig(Class<T extends Configurable<T>>)