i set permissionSystem = "luck_perms"
maxPlayerClaimsPermission = "xaero.pac_max_claims"

in luckperms:

meta.xaero.pac_max_claims.12
meta.openpartiesandclaims.xaero.pac_max_claims.12
.xaero.pac_max_claims.12
openpartiesandclaims.xaero.pac_max_claims.12

and it still dont work. I dont know what to do. Is it loads only after server restart?

You need to edit the OPAC config file with the server stopped and then start it, to make sure it is not overridden.
As for whether you're using Luck Perms correctly, I'm not an expert on that. Looks right to me.