AzureStorage.Queue.create_message

You're seeing just the function create_message, go back to AzureStorage.Queue module for more information.
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create_message(context, queue_name, text, options \\ [])

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The Put Message operation adds a new message to the back of the message queue.

A visibility timeout can also be specified to make the message invisible until the visibility timeout expires. A message must be in a format that can be included in an XML request with UTF-8 encoding. The encoded message can be up to 64 KiB in size for versions 2011-08-18 and newer, or 8 KiB in size for previous versions.

ref. https://docs.microsoft.com/en-us/rest/api/storageservices/put-message

context |> create_message("booking-queue", "hello world")