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

Question

Hi Appian, 
 
 In our middleware server&rsquo;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&rsquo;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

Shubham Aware · Answer

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.

Harsha Sharma · Answer

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