Upon parking the car, the driver found that the mobile app used to pay for parking was not functioning and they were unable to pay for parking. Upon return the application was still not working so they left. On the 14th October I, the registered keeper, received the PCN through the post (dated as issued on the 2nd of October).
Attached is the PCN received:


I do not have photos of the signs within the carpark but I can go and fetch them if it would be helpful. Unfortunately the images from google maps are from 2017 and seem to have old signage. There are no machines to pay for parking at this carpark and it is entirely app based. Opening the app and attempting to select the car park showed a modal with "timeout" making the application unusable. I've attached an example of the message shown on the application (reproducable today).