Editting field collections with service api
You must send acceptable field structure in order to create or edit the node

try to understand the field structure through Implementing hook_node_insert in custom module and  watchdog the inserted node via watchdog and you will have the structure drupal uses to insert then build it when you create/edit node through services   

function hook_node_insert($node){
  watchdog('node', json_encode($node));
}


after adding a node of the same type open dblog in your project and see that log, you could use pro.jsonlint  to understand it well

Hope that helps