failed to display Blue Badge - Enfield council

I have parked on the street to take my son for an appointment. He is disabled, and the Blue Badge is in his name. I forgot to put out the badge and when I returned to do it few minutes later, I already had the notice on the vehicle. The parking attendant was still there so I told him I forgot to display the Blue Badge and what should I do. He said to appeal and they will cancel it. But reading other fora I see that there seem to be not much I can do. I put it here for advice if it is worth appealing. The PCN and the signage pics are here: ,
Thank you, Chris.

This is a council PCN so I have moved this post to the Civil penalty charge notices (Councils, TFL and so on) forum.

To help the users there provide you with the best advice, please read the following thread carefully and provide as much of the information it requests as you are able to: READ THIS FIRST - **BEFORE POSTING YOUR CASE!**, This section is for council, TFL, Dart/Mersey/Tyne etc. cases