Creating a token for a new user fails

I have a registered user.
User clicks a button to connect his/her first mailbox.
Using a `button_to` I link to my controller.

But I run into an error.

Upon inspection of the params etc. callback_url IS passed
and contains a valid value ( `http://dubdub.bla/endpoint` ).

The default `:post` value in `connect_token_collection` crashes the app.

After some trial and error I replace `:post` with a hardcoded `:get`.
Result: `:get` returns a valid response containing a json object ( `[{token:"...",email:"..."},...]` )
but also results in an error ( see below ).

This piece of code calls the API request.
The request raises an error.

```ruby
# connect_token_collection.rb

  def create(callback_url, options={})
      # upon execution of this line things go wrong in connect_token.rb
      result_hash = api.request(
        :post,
        resource_url,
        options.merge(callback_url: callback_url)
      )

      result_hash.delete('success')

      resource_class.new(api, result_hash)
    end

```

with `:get`
```
NoMethodError - undefined method `keys' for #<Array:0x007f832602b808>:
  (gem) contextio-1.2.1/lib/contextio/api/resource.rb:91:in `validate_options'
  (gem) contextio-1.2.1/lib/contextio/api/resource.rb:20:in `initialize'
  (gem) contextio-1.2.1/lib/contextio/connect_token_collection.rb:41:in `new'
  (gem) contextio-1.2.1/lib/contextio/connect_token_collection.rb:41:in `create'
```

with `:post`
````
Started GET "/users/connect_mailbox" for xx.xx.xx.xx
Processing by RegistrationsController#connect_mailbox as HTML ( also tried as JS )
Completed 500 Internal Server Error in 686ms

ContextIO::API::Error - Missing required argument callback_url:
  (gem) contextio-1.2.1/lib/contextio/api.rb:104:in `request'
  (gem) contextio-1.2.1/lib/contextio/connect_token_collection.rb:33:in `create'
  app/controllers/registrations_controller.rb:11:in `connect_mailbox'
```

This is how I'm calling the code.
```ruby
class RegistrationsController < Devise::RegistrationsController
	# not sure if this is necessary - didn't get that far :)
	protect_from_forgery :except => :connect_mailbox # stop rails CSRF protection for this action

	respond_to :json

	def connect_mailbox
		contextio = ContextIO.new(ENV['GIN_CONTEXT_IO_KEY'],ENV['GIN_CONTEXT_IO_SECRET'])
		callback_url = "http://xxxxxxx/providers/connect-mailbox"
		tokens = contextio.connect_tokens
		response = tokens.create(callback_url)
		respond_to do |f|
			f.js
		end
	end
end
```