Slack API POST message code example

Example 1: slack message curl

curl -X POST -H 'Content-type: application/json' --data '{"text":"Allow me to reintroduce myself!"}' YOUR_WEBHOOK_URL

Example 2: how to send message with image to slack channel using java

"attachments": [{
    "fallback": "The attachement isn't supported.",
    "title": "VALENTINE'S DAY OFFER",
    "color": "#9C1A22",
    "pretext": "Today's list of awesome offers picked for you",
    "author_name": "Preethi",
    "author_link": "https://www.hongkiat.com/blog/author/preethi/",
    "author_icon": "https://assets.hongkiat.com/uploads/author/preethi.jpg",
    "mrkdwn_in": ["text","fields"],
    "text": "Just click the site names and start buying. Get *extra reduction with the offer code*, if provided.",
    "thumb_url": "http://example.com/thumbnail.jpg"
}]