Help adding mobs to pettable list

I'm not sure if I'm doing it right, but I can't seem to make iron golems pettable. I'm trying "/tag @e[type=minecraft:iron_golem] add pettable_anyway" and it says it's adding them, but it still doesn't let me. Could you please tell me the whole command I need to do?

I think it would be really helpful if the actual command was on the Modrinth page instead of just the tags.

Thanks x