Ruby on Rails: ActiveModel::ForbiddenAttributesError with strong params

In my RoR application, I have an update_multiple method that updates multiple records with the user's inputs. However, for some reason I get the error ActiveModel::ForbiddenAttributesError despite using strong params. Can someone please help me fix this?

The update_multiple method in Recipients_Controller is as follows:

def update_multiple
    @email = Email.find_by_id(params[:email_id])
    if Recipient.update(params[:recipient].keys, params[:recipient].values)
        @listofcontacts = Recipient.where("id in (?)", params[:recipient].keys)
        @account = Account.find_by_id(@email.account_id)
        @listofcontacts.each do |f|
            recipient_message = @email.message
            recipient_message = recipient_message.gsub("VAR1", f.var1)
            contact = Contact.find_by_id(f.contact_id)
            @unsubscribe = Rails.application.message_verifier(:unsubscribe).generate(contact.id)
            UserEmails.send_email(@email, @account, contact.email, @unsubscribe, recipient_message).deliver_now
        end
        flash[:notice] = "recipients were updated"
        redirect_to root_path
    else
        render 'edit_multiple'
    end
end

private
def recipient_params
  params.require(:recipient).permit(:contact_id, :group_id, :email_id, :var1, :var2, :var3)
end

This method takes the user input from this form:

<%= form_for :recipient, :url => update_multiple_recipients_path, :html => { :method => :put }  do %>
    <fieldset>
        <table cellpadding="0" cellspacing="0" border="0" class="table table-striped table-bordered" id="example">
            <thead>
            <tr>
                <th>Contact</th>
                <% if @email_message.upcase.include? "VAR1" %><th>VAR1</th><% end %>
            </tr>
            </thead>
            <tbody>
                <%= hidden_field_tag :email_id, @email %>
                <% @recipients.each do |recipient| %>
                    <tr class="odd gradeX">
                        <%= fields_for "recipient[]", recipient do |recipient_fields| %>
                        <td><%= recipient_fields.label recipient.contact.firstname %> <%= recipient_fields.label recipient.contact.surname %></td>
                        <% if @email_message.upcase.include? "VAR1" %><td><%= recipient_fields.text_field :var1, :required => true, :maxlength => 20 %></td><% end %>
                        <% end %>
                    </tr>
                <% end %>
            </tbody>
        </table></br>
        <%= submit_tag 'Send Email', {:class => 'btn btn-primary'} %></br>
        <%= link_to "Back", edit_email_path(@email) %>
    </fieldset> 
<% end %>

I really cannot figure out why I am getting this error. Can someone please help me?

I have looked at various other SO questions and they seem to have been solved by strong_params, but mine already has strong_params declared and isn't working.