How to get rid of MPs?

I've almost the event quest for Halloween. The only thing is I need 1080 Max Particles. I have 960. My problem: my inventory for Max Particles is full and I cannot find a way to delete or spend them. All the Dynamax Powerspots in the Area are Gangar and I'm nowhere near strong enough to battle him. Every time I try all my Pokémon are one shotted. Somehow, that results in me not having to pay the fee for trying to fight Gangar, so my MP storage is still full. What to do?