Welcome to the Community!
Can I please confirm if you've checked your solar inverter to ensure that it is turned on and that no warning lights are present?
I checked and found the inverter isn’t working for the last quarter..
That is why I am missing feed in tarrif credit.
Many advice you can provide to rectify it, please?
It's good to here that you've narrowed down the cause, definitely a step in the right direction!
I'd encourage you to first consult any instructions/paperwork for the inverter that you were given when the system was installed. If this fails, a call directly to the installer can help to!