EFK Stack on Kubernetes - Collecting logs from default namespace

Hi, I am using EFK stack on Kubernetes, I want to configure fluentd to collect logs from one specific namespace, the default namespace.
This is my fleuntd config file:

<label @FLUENT_LOG>
      <match fluent.**>
        @type null

      @type tail
      path /var/log/containers/*.log
      pos_file /var/log/app.log.pos
      tag kubernetes.*
      read_from_head true
        @type json
        time_format %Y-%m-%dT%H:%M:%S.%NZ

    <filter kubernetes.**>
        @type kubernetes_metadata

    <filter kubernetes.**>
       @type grep
            key log
            pattern (.\[notice]\.*|^[ \\\/\(\)\*\|_]+(?!.*[a-zA-Z0-9]).*$|^\s*$|.*GET*|.*POST*)
            key kubernetes.namespace_name
            pattern /^default$/
    <match ** >
       @type elasticsearch_dynamic
       @log_level info
       include_tag_key true
       scheme "#{ENV['FLUENT_ELASTICSEARCH_SCHEME'] || 'http'}"
       ssl_verify "#{ENV['FLUENT_ELASTICSEARCH_SSL_VERIFY'] || 'true'}"
       reload_connections true
       logstash_format true
       logstash_prefix logstash
           @type file
           path /var/log/fluentd-buffers/kubernetes.system.buffer
           flush_mode interval
           retry_type exponential_backoff
           flush_thread_count 2
           flush_interval 5s
           retry_forever true
           retry_max_interval 30
           chunk_limit_size 2M
           queue_limit_length 32
           overflow_action block

The way I tired to do that is by adding:

            key kubernetes.namespace_name
            pattern /^default$/

but is not working this way, fluentd is not collecting any logs.

I don't know if the question is for here but please help me if you know the answer.