How to use composition in builder pattern?

I have two types of payload coming from upstream: It's either PayloadA or PayloadB. There are some common fields between PayloadA and PayloadB so I created Payload class with those common fields and for rest I created two builder class one for each payload. In general they will have lot of fields.

Below is the builder class for PayloadA:

public final class PayloadA {
  private final String clientId;
  private final String langid;
  private final String deviceId;
  private final Map<String, String> applicationPayload;

  private PayloadA(Builder builder) {
    this.clientId = builder.clientId;
    this.langid = builder.langid;
    this.deviceId = builder.deviceId;
    this.applicationPayload = builder.applicationPayload.build();
  }

  public static class Builder {
    protected final String deviceId;
    protected String clientId;
    protected String langid;
    protected ImmutableMap.Builder<String, String> applicationPayload = ImmutableMap.builder();

    public Builder(String deviceId) {
      this.deviceId = deviceId;
    }

    public Builder setClientId(String clientId) {
      this.clientId = clientId;
      return this;
    }

    public Builder setLangid(String langid) {
      this.langid = langid;
      return this;
    }

    public Builder setPayload(Map<String, String> payload) {
      this.applicationPayload.putAll(payload);
      return this;
    }

    public PayloadA build() {
      return new PayloadA(this);
    }
  }

    // getters and to string here
}

Now below is the class for PayloadB:

public final class PayloadB {
  private final String clientid;
  private final String type;
  private final String payId;

  private PayloadB(Builder builder) {
    this.clientid = builder.clientid;
    this.type = builder.type;
    this.payId = builder.payId;
  }

  public static class Builder {
    protected final String type;
    protected String payId;
    protected String clientid;

    public Builder(String type) {
      this.type = type;
    }

    public Builder setPayId(String payId) {
      this.payId = payId;
      return this;
    }

    public Builder setClientId(String clientid) {
      this.clientid = clientid;
      return this;
    }

    public PayloadB build() {
      return new PayloadB(this);
    }
  }

    // getters and to string here
}

Now I have created another class which is Payload class (does this have to be abstract class?) in which I have all the common fields both for PayloadA and PayloadB so I have to set these fields as well somehow and I am not sure how to use below class:

public abstract class Payload {
  private long createTimestamp;
  private String key;

  // getters and setters here
}

Question:

Now from the below code I am making either PayloadA or PayloadB depending on what is passed.

  protected void run(String name) {
    // .. some code here

    if(name.equalsIgnoreCase("PayloadA") {
    PayloadA payload = new PayloadA.Builder(getDeviceId())
                                            .setClientId("someid")
                                            .setLangid("anotherid")
                                            .setPayload("some map")
                                            .build();
        DataProcessor.getInstance().process(payload);
    } else {
    PayloadB payload = new PayloadB.Builder(getType())
                                            .setPayId("someid")
                                            .setClientId("anotherid")
                                            .build();
        DataProcessor.getInstance().process(payload);

    }

    // .. some code here
  }

Now how can I set createTimestamp and key variable which is in Payload class? I have to set createTimestamp in the process method of DataProcessor. And key variable is determine from few fields either from PayloadA or PayloadB depending on what is set.

Should I have on big builder pattern class with everything in it or multiple builder pattern extending something like Payload class (which has common fields)?