alarm motion sensor 1st gen not pairing

i have a first gen motion sensor which will not pair.i have tried battery off for 10 mins,resetting it etc.i have added this device and got as far as take the tab out on the back of the sensor on the app.i have done this,the sensor has flashed 3 times in blue about 5 times thens goes off.i have just purchased this ssytem from ring and all the other ones are fine.can you help please.