Errors while importing data to ElasticSearch Index

I am importing around 8GB of data to ElasticSearch Index, after inserting few records ElasticSearch started showing the following exception

{ _index: 'todos',
  _type: '_doc',
  _id: '1649269184',
  status: 403,
  error:
   { type: 'cluster_block_exception',
     reason:
      'index [todos] blocked by: [FORBIDDEN/12/index read-only / allow delete (api)];' } }
{ _index: 'todos',
  _type: '_doc',
  _id: '1649268012',
  status: 403,
  error:
   { type: 'cluster_block_exception',
     reason:
      'index [todos] blocked by: [FORBIDDEN/12/index read-only / allow delete (api)];' } }