WebClient chat_postMessage doesn't support input blocks - errors with {'ok': False, 'error': 'invalid_blocks'}

[kbroughton]

WebClient chat_postMessage doesn't support input blocks.
This may be similar to #853 where an excessive input validation needed to be removed. #519 also looks mildly similar.

Category (place an x in each of the [ ])

• slack_sdk.web.WebClient (sync/async) (Web API client)

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 and it looked fine when selecting "Message Preview".

		{
			"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'}

If messages are not meant to support input fields, then the Message Preview should fail in Block Kit Tool. It doesn't.

Also, although the documentation for python says you need to urlEncode the JSON-based array, there is no example of using "blocks" in the python sample code, and the description at https://api.slack.com/methods/chat.postMessage#arg_blocks is incorrect. Documentation fix needed

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

I've created a gist to reproduce the issue https://gist.github.com/kbroughton/e46edc3f6454c8dc33a09431b5685a6c

[seratch]

Hi @kbroughton, thanks for writing in!

I've checked your gist and found that the reason why your code is getting "invalid_blocks" error code from the server side is that you have an input block element under an "actions" block, which is not available in Block Kit. Your app needs to have any blocks at the top level, not under a block.

You can see the detailed error in Block Kit Builder here.

Here is a working example in Block Kit Builder.

I hope this helps.

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