Java: PubsubMessage Subscriber receives message with no data or attribute

Question

I'm trying to receive message to a topic and receive the message in the subscriber. But in the subscriber I don't receive any message, only an empty PubsubMessage.

Subscriber

package com.dsam.assignment02.functions;

import com.google.cloud.functions.BackgroundFunction;
import com.google.cloud.functions.Context;
import com.google.pubsub.v1.PubsubMessage;

import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.logging.Level;
import java.util.logging.Logger;

public class OrderBillPdfGeneratorFunction implements BackgroundFunction<PubsubMessage> {
    private static final Logger logger = Logger.getLogger(OrderBillPdfGeneratorFunction.class.getName());

    @Override
    public void accept(PubsubMessage payload, Context context) throws Exception {
        String s = payload.getData().isEmpty() ? "No data" : new String(
            Base64.getDecoder().decode(payload.getData().toByteArray()),
            StandardCharsets.UTF_8
        );
        String t = String.valueOf(payload.getAttributesCount());
        logger.log(Level.INFO, String.format("Data: %s\nAttribute Count: %s", s, t));
    }
}

Log Output

Data: No data
Attribute Count: 0

Any idea what I'm missing here?

Update

I published message from cloud console pub/sub topic, but still didn't receive any data, which rules out the possiblity of issue being related to the publisher code.