send: add peer message metadata node (#972)

send.go

@@ -1049,7 +1049,12 @@ func (cli *Client) preparePeerMessageNode(
 	if err != nil {
 		return nil, fmt.Errorf("failed to encrypt peer message for %s: %v", to, err)
 	}
-	content := []waBinary.Node{*encrypted}
+	content := []waBinary.Node{{
+		Tag: "meta",
+		Attrs: waBinary.Attrs{
+			"appdata": "default",
+		},
+	}, *encrypted}
 	if isPreKey && cli.MessengerConfig == nil {
 		content = append(content, cli.makeDeviceIdentityNode())
 	}