Slack API invalid_block - slack-api

Question

I'm building a simple slack bot and I am playing with the checkboxes element.
When I return the following from my API in a JSON response to a slash-command I get an error failed with the error "invalid_blocks", however, when I put this in the block-kit-builder it works perfectly (including "sending to slack" button)
Any ideas why this is failing when I run my slash command - and is it possible to see more detailed error messages from slack?
{
"blocks": [
{
"elements": [
{
"style": "primary",
"text": {
"emoji": true,
"text": "Create new TODO list",
"type": "plain_text"
},
"type": "button",
"value": "value"
},
{
"style": "primary",
"text": {
"emoji": true,
"text": "Help",
"type": "plain_text"
},
"type": "button",
"value": "value"
}
],
"type": "actions"
},
{
"text": {
"text": "Today",
"type": "mrkdwn"
},
"type": "section"
},
{
"elements": [
{
"initial_options": [
{
"text": {
"text": "Get Into the garden",
"type": "mrkdwn"
},
"value": "foo"
}
],
"options": [
{
"text": {
"text": "Get Into the garden",
"type": "mrkdwn"
},
"value": "foo"
}
],
"type": "checkboxes"
},
{
"style": "primary",
"text": {
"emoji": true,
"text": "Add new Task",
"type": "plain_text"
},
"type": "button",
"value": "value"
}
],
"type": "actions"
}
],
"type": "home"
}

Answer 1

I am using the Slack Web API. I was getting the similar error. After a lot of looking around, here's how I solved it.
import json
blocks = [{...}]
payload = {
"blocks": json.dumps(blocks)
}
You will then send this payload.

Answer 2

in the api, the "blocks" parameter need to be string type. Did you convert it to string or you use it as a JSON ?
https://api.slack.com/methods/chat.postMessage

Answer 3

In the Block Kit Builder, the data is a JSON with a blocks key.
In the Slack API, the blocks param is only the list of JSON objects.
blocks = [
{
"text": {
"text": "Its the list of your blocks",
"type": "mrkdwn"
},
"type": "section"
}
]
text = 'Alternative data in text'
client.chat_postMessage(channel=channel_id, blocks=blocks, text=text)

Answer 4

Another cause of this problem seems to be too many blocks being returned. I can't find any documentation about this whatsoever, but personal experience seems to indicate about 20 blocks is the maximum.
An alternative is to return fewer blocks, with paging actions -- paging works well with the "replace" message so that the content being paged through does not result in many separate messages.

Answer 5

It appears that not all valid elements in block kit tool can be posted as a message, despite the fact that message preview works fine in the Block Tool.
In my case, the code failed when I included an input block and passed when i removed it. The input block was generated by the Block Kit tool.
{
"type": "input",
"element": {
"type": "plain_text_input",
"action_id": "plain_text_input-action"
},
"label": {
"type": "plain_text",
"text": "Feedback",
"emoji": true
}
}
The error was
{'ok': False, 'error': 'invalid_blocks'}
Also, although the documentation for python says you need to urlEncode the JSON-based array, there is no example, and it is incorrect. https://api.slack.com/methods/chat.postMessage
You can see on line 29 in the SDK test code below that blocks= takes a regular list of dicts not a string.
https://github.com/slackapi/python-slack-sdk/blob/c9dc6aa0907a72c16cf36aa15e7e80031a9fdce2/integration_tests/samples/basic_usage/sending_a_message.py