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yongsungk0001
August 28, 2025
Question

We are encountering a 400 error when calling the Appian Web API from our middleware server.

  • August 28, 2025
  • 2 replies
  • 0 views

Hi Appian,

In our middleware server’s integration solution, we are calling an Appian Web API but receiving a 400 error.

However, when we test the same Appian Web API call using curl from the middleware server, it works fine with a 200 response.

Since there seems to be no difference between the two calls, I’m not sure why the 400 error occurs.

If you have had a similar experience and resolved it, I would appreciate your advice.

Thank you

    2 replies

    shubhama926776
    shubhama926776
    August 28, 2025

    Most common causes for your 400 error when curl works:
    Header differences -> Your middleware might be sending Content-Type: application/json; charset=utf-8 while curl sends just application/json. Try removing charset specification.
    Request body encoding -> Check for extra whitespace, BOM characters, or different JSON formatting between your middleware and curl requests.

    To debug precisely, capture the exact request from your middleware and compare it byte-by-byte with the working curl request.

      harshas2775
      harshas2775
      August 29, 2025

      In addition to what Shubham suggested, check if the error log (logs/design_errors.csv) has additional details. 

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