How can I add document by api?

API
1

https://api.swiftype.com/api/v1/engines/enginename/document_types/stores/documents.json?auth_token=MyAPIKey&document={“external_id”:“1”,“fields”:[{“name”:“title”,“value”:“Mat %26 Max”,“type”:“string”}]}

I tried to add document using the api like the above.
But I received the following response.

{
“error”: “Internal server error. Please email support@swiftype.com if this error persists.”
}

Plz solve this problem.
Thanks.