petrol 2007 Subaru Legacy Outback . Key will not start car

Since late December turning the key will not start my car and I called out the AA Home Start as this happened at home and paid the home start fee of over £70 . AA engineer got the car going by entering a four digit code twice in close succession  into the panel that drops down from below and to the right of steering wheel . I had made a note of the four digit code in my phone and operating instruction book as coincidentally the same problem happened two years earlier almost to the same date  .In December 2022 the dealer charged over £120 for their work and it did not happen again until just before Christmas 2024 .Since then I have been doing this coding in the number however sometimes the car starts off the key but then quits requiring me to put the code in twice and then turn the key and the engine fires up . Mistype the code can cause the car to be isolated for up to 30minutes . I have tried the unused battery in the key and same applies . Tomorrow I will get a new battery and insert into the key and hope this will sort out the problem. Can anyone help please .