[SOLVED] Web version of Postman with browser agent works, but the postman desktop app and with web app with desktop agent get 503 errors

Web version of Postman with browser agent works, but the postman desktop app and with web app with desktop agent get 503 errors

I am using postman trying to post a basic http request to an API endpoint. My web version (Postman for Web Version 9.0.9-211111-0900 Chrome 95 / Windows 10) can do this successfully everytime (http 200). My desktop application version (Postman v9.1.3) cannot. I also have the same problem with the web version of postman when I turn the Desktop Agent (v0.3.9) on. The postman desktop application and the postman web with desktop agent on I get the following http 503 error. Any ideas why this is happening?

<html style="height:100%">

<head>
    <META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">
    <meta name="format-detection" content="telephone=no">
    <meta name="viewport" content="initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
</head>

<body style="margin:0px;height:100%"><iframe id="main-iframe"
        src="/_Incapsula_Resource?CWUDNSAI=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx&mth=POST"
        frameborder=0 width="100%" height="100%" marginheight="0px" marginwidth="0px">Request unsuccessful. Incapsula
        incident ID: 0-xxxxxxxxxxxx</iframe></body>

</html>

Solution

I found that the 503 error was being caused by auto generated hidden header settings of my postman message.

The issue was that the hidden Host header was unchecked. After checking that off and resending it worked. It worked both with the desktop app and the web app with the desktop client turned on.