通过SendGrid v3发送HTML内容

I use GO and I try send mail via sendgrid API v3(https://github.com/sendgrid/sendgrid-go Without Mail Helper Class). But when i use this code:

"content": [
    {
      "type": "text/html", 
      "value": "<html><head></head><body>Hello You link <a href="http://example.com/reschedule?id=12334">Click</a></body></html>"
    }
  ], 

i get error:

400 {"errors":[{"message":"Bad Request","field":null,"help":null}]}

But this code works correctly:

"content": [
    {
      "type": "text/html", 
      "value": "<html><head></head><body>Hello!</body></html>"
    }
  ], 

I think problem in special characters, but how i can fix it? Thank you!

Need do this:

<div class=\"ad_box\"><img class=\"banner\" src=\"some_ad.png\" alt=\"\" \/>

Example
    "content": [
        {
          "type": "text/html", 
          "value": "<html><head></head><body>Hello You link <a href=\"http://example.com/reschedule?id=12334\">Click</a></body></html>"
        }
      ],