meteor-shopify : expected String to be a Hash

I'm using froatsnook:shopify trying to modify a custom collection's metafields.

Server JS

/**
 * Modify Shopify Custom Collection Metafields
 * @request PUT /admin/custom_collections/#{id}.json
 * 
 * @param  {Number}   collection_id 
 * @param  {Object}   collection_data
 * @param  {Function} callback
 */
modifyShopifyCustomCollectionMetafields: function(collection_id, collection_data, callback) {

  var meta = ShopifyAPI.modifyCustomCollection({
    id: collection_id,
    custom_collection : JSON.stringify( collection_data )
  })

  if ( AdminConfig.debug.server ) console.log( 'modifyShopifyCustomCollectionMetafields', meta )

  if ( callback ) callback( meta )

  return meta;

},

Client JS

Meteor.call('modifyShopifyCustomCollectionMetafields', collection_id, {
  'id': collection_id,
  'metafields' : [
  {
    'key' : 'color_primary',
    'value' : design_settings.colors.primary,
    'value_type' : 'string',
    'namespace' : 'store',
  },
  {
    'key' : 'color_dark',
    'value' : design_settings.colors.primary_dark,
    'value_type' : 'string',
    'namespace' : 'store',
  },
  {
    'key' : 'color_light',
    'value' : design_settings.colors.primary_light,
    'value_type' : 'string',
    'namespace' : 'store',
  },
  ]
}, function (data) {
  console.log( 'Clientside callback', data )
})

All looks fine to be, but then I get this in the (server) console:

PUT https://<MY_STORE_NAME>.myshopify.com/admin/custom_collections/42393729.json?custom_collection={"id":"42393729","metafields":[{"key":"color_primary","value":"#5c28a4","value_type":"string","namespace":"store"},{"key":"color_dark","value":"#401a74","value_type":"string","namespace":"store"},{"key":"color_light","value":"#a42da8","value_type":"string","namespace":"store"}]}

Exception while invoking method 'modifyShopifyCustomCollectionMetafields' Error: failed [400] {"errors":{"custom_collection":"expected String to be a Hash"}}

Note that if I remove JSON.stringify(...) from the serverside JS, it will try to send [Object object] in the request URI.

Any ideas?

Copyright Notice：Content Author:「elzi」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/30767554/meteor-shopify-expected-string-to-be-a-hash