Thanks for providing some extra information about some of the constructs of the form and how the textarea field’s value is converted to a variable, but it’s still unknown how the actual request is being created / assembled before being sent to the API endpoint.
HOW does the request get sent? WHAT is sending it? Some JavaScript? A browser add-in? Something else?
To be blunt, a 400 error with an INVALID_INPUT is simply the API telling you that the body of the request contains mal-formed JSON (such as the missing inverted commas around the text string object I’ve already mentioned) and it can’t process it. Here is a similar thread on the same topic.
What sanitisation / stringification is done to the descriptionText variable to encode any special characters? What is done to convert the string variable into ADF formatted JSON for use in the request body?
Testing your JSON request body with a tool, like this one , will immediately show you where the problem lies. Tools like this one will even fix the faulty JSON and tell you where the fault was.
Once you have confirmed that the JSON request body is correct, you can use the Document Viewer tool to test if the ADF is structured correctly.