Assuming:

class Person < ActiveRecord::Base
    scope :domestic, ->(countries) { where(country: countries) }
    def self.ransackable_scopes(auth_object=nil); [:domestic]; end
end

Trying to filter by a list of countries:

Person.search(country: ['US', 'JP'])

Will raise ArgumentError: wrong number of arguments (2 for 1)

Again, we are able to format the input in order to avoid this.

Person.search(country: [['US', 'JP']])

This avoids the issue as it seems to be a problem with splatting the args.