Intermittent starting fault

[Nball]

Good afternoon after a little advice
I have a 2002 9n polo 1.9tdi.when I start the car after a period of a day or so when I haven’t used it it starts up fine, several journeys in a short space and it won’t start, I get the flashing car on the dashboard, it will turn over but cuts out, I’ve been told it could be a transponder fault, if this is the case is it as simple as ordering a new ignition or does anyone think it maybe something else, obviously I don’t want to order the barrel and it’s a non refundable part

[Maarten]

Flashing car means key transponder not correct for car, or unreadable.
Did you try the spare key if you have it?