Help with no start PLEASE.

[Ozruss90]

Removed cam position sensor to rectify an oil leak. Seamed a simple job. 1 bolt removed and the sensor just fell out . No resistance from the O ring. On inspection the sensor looked to be in perfect condition so wiped clean, new O ring and back in.
Now the engine will crank and start, BUT dies instantly try numerous times and does the same. Starts and dies instantly.
Any suggestions on what I may have done wrong or how to proceed, to sort out problem.

TIA.
Cheers.
Russell 🇦🇺