As it was my first ever Tesla charge ( and I was desperate for the loo ) I was all over the place. Tried the app but as you say, no signal. Tried contactless but couldn't really see the screen properly so not sure if that had worked. Had seen complaints about no signal and having to use Arundel wi-fi. Hadn't made a note of the password and couldn't get back to it due to no signal. BUT the gent in the shop was very accommodating and only too happy to let me use the excellent wifi. Also loo is in coffee shop if required.
Finding it was a challenge. It is actually on The Arundel hotel carpark. Plenty of chargers. Readily available out of season.