save checkbox value once it tick in rails

In my app I Have check boxes and want to save checkbox value once check box tick and page reload. Here is my custom_field_update action.

def custom_field_update
begin
  val = params[:field_value]
  alt = params[:alt_text]

  if alt
    if alt.kind_of?(Array)
      alt = alt.join(',')
    end
  else
    alt = ""
  end

  if val.kind_of?(Array)
    val = val.join(',')
  end

  @url = api_version_root+'/startups/fields/'+params[:sid]
  response = RestClient.put @url,
    { startup_field: {
                      id: params[:sid],
                      alt_text: alt,
                      field_value: val,
                      user_id: current_user
                    }
    }, api_token_hash

  flash[:info] = "Custom field updated."
  redirect_to :back and return
rescue RestClient::ExceptionWithResponse => err
  handle_rest_error http_code: err.http_code
end
end

Here is my checklist

<%= form_tag({controller: "srm", action: "custom_field_update"}, method: "post", multipart: true ) do %>
<input type="hidden" name="sid" value="<%= m["id"] %>">
  <% templat = @custom_templates.select{|s| s["id"] == m["startup_field_template_id"]}.first%>
  <small>
       <% vals = field["options"].to_s.gsub(/[\[\"\]]/, '').split(',') %>
       <% vals.each do |v| %>
          <% if val.include?(v.to_s) %>
           <input type="checkbox" checked="checked"  />&nbsp;&nbsp;&nbsp; <%= v %><br/>
          <% else %>
            <% if templat["option_multi"] %>
              <input type="checkbox" />&nbsp;&nbsp;&nbsp; <%= v %><br/>
            <% else %>
              <input type="checkbox" class="check" id="check"/>&nbsp;&nbsp;&nbsp; <%= v %><br/>
            <% end %>
         <% end %>
     <% end %>
  </small>
  <% end %>

But this is not work. Can anyone help me for this?