Error: Data structure returned is not convertible in the requested format: Only integer keys supported for array columns on base level. Unsupported string 'searches' found for row 'array (
  0 => 
  array (
    'keyword' => 'checkpoint',
    'searches' => 1,
  ),
  1 => 
  array (
    'keyword' => 'snapshot',
    'searches' => 1,
  ),
)'. Try to call this method with the parameters '&format=original&serialize=1'; you will get the original php data structure serialized.