The wiring looks right. Although based on the manual, the siren should be wired prior to powering up and pairing with the panel.
However, based on previous user experience and troubleshooting, there may be an issue when using wireless activation that limits output. Although there has been no word on whether or not this a bug or by design.
In this case, using the wired input method should work. See optional wiring here in the manual here.