Ring outdoor siren hardwire

Hi everyone,

My electrician tried to hardwire my Ring outdoor siren using this transformer https://www.screwfix.com/p/british-general-fortress-8-24v-ac-8va-bell-transformer-module/8707P. We get 12V in the siren, but it doesn’t work. We tried two different sirens and still doesn’t work.

Has anyone managed to hardwire the Ring outdoor siren with a transformer and what transformer did they use? Any recommendation is really appreciated.

I am not looking for the Plug-In Adapter since access to a socket is difficult and the wiring is already done.