SendGrid v3 Api dynamic template_id not recognised, won't send

Question

I am trying to send a simple password reset email that's defined in a dynamic template. I have tested the template within SendGrid and it works fine. I have copied and pasted the template_id from the website, checked and double-checked it, but trying to post this message:

{
    "personalizations": [
        {
            "to": [
                {
                    "email": "chairman@##########.org.uk"
                }
            ],
            "dynamic_template_data": {
                "firstname": "Tim",
                "url": "https://localhost:5001/account/ProcessPasswordReset?id=4&code=############"
            },
            "send_at": 0
        }
    ],
    "from": {
        "email": "membership@##########.org.uk",
        "name": "A Person"
    },
    "reply_to_list": [],
    "subject": "Password Reset",
    "content": [],
    "template_id": "d-23a2c68a9e5349488be23299a04a9485",
    "send_at": 0
}

I get the following response

{
    "errors": [
        {
            "message": "Unless a valid template_id is provided, the content parameter is required. There must be at least one defined content block. We typically suggest both text/plain and text/html blocks are included, but only one block is required.",
            "field": "content",
            "help": "http://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/errors.html#message.content"
        }
    ]
}

As far as I can tell from the documentation, this is a well-formed message with a correct template_id.

Answer 1

Ok so the problem was the empty

"content": [],

This must not be sent at all if there is no content to send. Working as expected now this is removed.