GroupNexus the gym group PCN

"Other" - your first suggestion says who was driving...

Just an update, they cancelled the PCN,
However fyi although I did use the above template, I did also attach a screenshot of gym membership/attendance

They replied "as you are a gym member..."
so I think that was probably the main reason for them allowing the appeal?

Good news - yep, where you have a meritorious appeal point that you can use without undermining other arguments you might need later, there's seldom any harm in including it! In this case, I would wager that they have some sort of clause in their contract requiring them to cancel for genuine members.