Messaging.Publish from Business logic

I want to send a push notification from Business logic to all devices the same way as we can do by ticking Broadcast checkbox in Messaging tab in the Backendless dashboard.
I was following this guide for publishing push messages to devices (except that I set Push broadcast to PushBroadcastMask.ALL), but the problem is that the message isn’t sent to the device which is subscribed to a custom channel. Instead, the default channel is created and all messages are going to that channel.

You can specify the channels to which you want to send the messages, but you can’t specify “ALL” channels.