Q:

Slack send attachment returning 500 error

I am trying to send an attachment to a Slack web hook.  
I have followed the API documentation and can send a simple message.  When I try send an attachment I get a 500 error, I presume there is an issue with my payload but I cannot work it out for the life of me. 
How do I get the attachment to post successfully? 
import slackweb

slack = slackweb. Slack(url='WEB HOOK URL HERE')

slack.notify(text="Maguro is a sushi")

attachments = []
attachment = {
    "attachments": [
        {
            "fallback": "Required plain-text summary of the attachment.", 
            "color": "#36a64f",
            "pretext": "Optional text that appears above the attachment block",
            "author_name": "Bobby Tables",
            "author_link": "http://flickr.com/bobby/",
            "author_icon": "http://flickr.com/icons/bobby.jpg",
            "title": "Slack API Documentation",
            "title_link": "https://api.slack.com/",
            "text": "Optional text that appears within the attachment",
            "fields": [
                {
                    "title": "Priority",
                    "value": "High",
                    "short": False
                }
            ],
            "image_url": "http://my-website.com/path/to/image.jpg",
            "thumb_url": "http://example.com/path/to/thumb.png",
            "footer": "Slack API",
            "footer_icon": "https://platform.slack-edge.com/img/default_application_icon.png",
            "ts": 123456789
        }
    ]
}

attachments.append(attachment)
slack.notify(attachments=attachments)

A:

You're missing two required fields in your Slack message with attachments: text and channel.  You also need to lowercase the value of the short field to false.  
See the corrected message here in Slack's message tester:
{
    "text": "You need this field",
    "channel": "C########",
    "attachments": [
        {
            "fallback": "Required plain-text summary of the attachment.", 
            "color": "#36a64f",
            "pretext": "Optional text that appears above the attachment block",
            "author_name": "Bobby Tables",
            "author_link": "http://flickr.com/bobby/",
            "author_icon": "http://flickr.com/icons/bobby.jpg",
            "title": "Slack API Documentation",
            "title_link": "https://api.slack.com/",
            "text": "Optional text that appears within the attachment",
            "fields": [
                {
                    "title": "Priority",
                    "value": "High",
                    "short": false
                }
            ],
            "image_url": "http://my-website.com/path/to/image.jpg",
            "thumb_url": "http://example.com/path/to/thumb.png",
            "footer": "Slack API",
            "footer_icon": "https://platform.slack-edge.com/img/default_application_icon.png",
            "ts": 123456789
        }
    ]
}

Create a JSON structure including those two fields and your attachments variable, and you should be good to go.