How to check if I have some error in my hash

I try to check if I have an error in my token, In my view it works like this and it seems to be Ok :

<% if @token['error'].present?%>
    <%= @token['error']%> // display the message of the error
    <%= flash[:error]%> //display ERROR
    <% else %>
    <%= @token%> // display the token
    <p>Ok</p>
<%end%>

But in my controller, I can't do that :

 if @token['error'].present?
            flash[:error] = "ERROR"
        else
            @token = HTTParty.post('https://mooncard23-sandbox.biapi.pro/2.0/auth/token/access', 
                body: {
                    client_id: XXXXXXXXXX,
                    client_secret: "YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY",
                    code: @decoded_code
                }
            ) 
 end  

I have the error "undefined method `[]' for nil:NilClass". Do you know how to check if my token return an error ?