Ring Siren Hardwire Issues

Hello,I recently got a Ring Siren and a 2nd gen plug in adaptor, and I'm really struggling to get the alarm to recognise its been hardwired in. I've managed to set up the Siren, I've connected the adaptor correctly as far as I can tell and the Siren just doesn't recognise its hardwired in. The internal socket works (I've tried alternative devices in it). I initially thought I may have mixed up the +/- on the adaptor (they're both white and unhelpfully not marked), but even after switching them around, still nothing. Am i missed something blindingly obvious, or do I have faulty hardware?Any help is massively appreciated.Jamie