Twice my Spider has failed to start. Both times the weather was hot and the car had been driven hard, so the engine compartment was hot too. In both cases I tried to start it without any significant pause after I inserted the key device. I'm not sure if that was the cause or not. The instrument lights and indications were normal but the starter would not engage but the lights would dim a bit and there was a bit of a "click". Of course I tried several times.
In both cases, after removing and re-connecting the battery leads (no help) and tapping the starter solenoid, the car started. Was waiting while the engine compartment cooled off the cure, or was tapping the solenoid helpful? Who knows? When I got home I didn't find any error codes.
I cleaned and lubricated the starter and solenoid and it hasn't failed since. Unfortunately, the solenoid is sealed so I couldn't gain access to the contactor, which is usually the reason for this kind of behavior.