I am paying monthly subscription but the features have stopped working. I try and click to re-subscribe but it says I have already subscribed. I have tried logging out and back in to light room and I have rebooted my iPhone.
That error means you have have signed into Lightroom with another account (based on another email address or social sign in method), and it is the other Lightroom account that can use the paid subscription. The error exists to prevent you from paying for the same subscription twice.
I will send you a private message with some additional advice.