Where is the point of contract when using a pay and display ticket?

The machine states 'display within vehicle' but the ticket states 'display on dashboard'.

Whilst I have a ticket which was 'forgiven' I did wonder where the contract between myself and the council started. I can't agree to the terms after I've purchased a ticket. My understanding of contract law is that it's only valid if the terms are known beforehand and can be rejected.

Obviously paying for a ticket and seeing the 'display on dashboard' text means I had no opportunity to decline if I chose not to display on the dashboard but on a windscreen clip.

I can't find anywhere that this is defined in law.

Thanks

Peter

Nothing to do with contract law, the Ts and Cs of use of the car park are made under local legislation(a Traffic Order made pursuant to s32 Road Traffic Regulation Act).

The PCN itself was issued under statutory powers.