Getting unpermitted parameter using collection_select with multiple => true

I have two models with no associations between them. I am fetching the list of names as options for selection to the primary model. Collection_select without multiple => true works as expected. But when i add multiple i get the unpermitted parameter error.

Because :conf_string is an array, so you need to permit it as an array.

In your BaseTablesController:

def base_table_params
  params.require(:base_table).permit(:name, conf_string: [])
end

Don't forget to update :conF_string to :conf_string. I think you made a typing mistake