I decided to make a custom command for fun, similar to the /msg command. The code for the command is below:

public class PrivateMessageCommand {

	public static void register(CommandDispatcher<CommandSource> dispatcher) {
		dispatcher.register(Commands.literal("pm").requires((context) -> {
			return context.hasPermissionLevel(0);
		}).then(Commands.argument("targets", EntityArgument.players())
				.then(Commands.argument("message", MessageArgument.message()).executes((context) -> {
					ITextComponent itextcomponent = MessageArgument.getMessage(context, "message");
					int i = 0;

					for (ServerPlayerEntity serverplayerentity : EntityArgument.getPlayers(context, "targets")) {
						serverplayerentity.sendMessage(TextComponentUtils.func_240645_a_(context.getSource(), itextcomponent, serverplayerentity, 0), Util.DUMMY_UUID);
						++i;
					}

					return i;
				}))));
	}

}

It is supposed to work like the /msg command where the syntax of the command is the following:

/pm <targets> <message>

This works in single player but not on a realm/server, and I don't know why.

The message command can be used without permissions, which I tried to replicate here but returning a permission level of 0, however my command doesn't show up in the prompt when I type it while in a realm.

How do I go about getting my command to work on a server?

If I can't make custom commands from scratch, then is there a method in a class somewhere to execute a command, so I can just have my custom command run a vanilla command?

For example, /pm would just run /msg with the targets and the message.