Ring outdoor siren - power issue

My electrician arrived Friday and installed another security camera, latest one. (hard wired) He also installed the Ring Siren, the siren was wired with the Ring transformer and wire to an eklectircal sock (UK Mains). He also left in the batteries D type and inserted the rechargeable battery also. Today I called him back as the Siron wasn't recognised in the ring sustem, the tabs to the D battery had been removed. He took the D batteries out and the rechargeable battery also. After 30 seconds he put them back. At this stage the siren had, mains power on with Ring transformer, rechargeable battery in and D batteries in. The system managed to pair easily so I was quite pleased at this stage. But then I noticed the manins power, in the power options states, Not Connected. Before the electricain left he double checked the wiring and that the socket wasa live and switch on, they were. So I have a siren box fitted, I want it to be ion the mains as I am have paid the electricain for installing that. But Ring will not connect to the mains? I have tried going through the procedure in Ring again and when scanning the QR code it states device in system. Help please. Paul