Since the YN600EX-RT uses the Canon RT wireless radio protocol and the YN560 IV uses the older Yongnuo YN560/RF605/RF603 protocol, the YN600EX-RT can not communicate directly with the YN560 IV. They use the same wireless frequencies, but each uses a different "language" to communicate the same information.

The easiest solution would probably be to use a YNE3-RX receiver attached to the hot foot of the YN560 IV. That might allow you to set manual power remotely, but it might not. If the YNE3-RX doesn't fire the flash when directly attached to the YN560 IV hot foot, then you could either:

• Use a PC cord between the YNE3-RX and the YN560 IV to send a "fire" command. All adjustments to the flash settings would need to be made directly on the flash.
• Tape over the TTL contacts on the YNE3-RX and attach it to the hot foot of the YN560 IV. The receiver would only send a "fire" command to the flash via the main pin. All adjustments to the flash settings would need to be made directly on the flash.