Unable to retrieve license key: 502 - Web server received an invalid response while acting as a gateway or proxy server – Plesk Help Center

kb: fixed kb: bug ABT: Group A

Symptoms

When retrieving License Keys on Tools & Settings > License Management > Retrieve Keys below error is displayed in the browser:

CONFIG_TEXT: 502 - Web server received an invalid response while acting as a gateway or proxy server

or

CONFIG_TEXT: This site can't be reached ERR_RESPONSE_HEADER_TOO_BIG
In the /var/log/plesk/sw-cp-server/error_log:

CONFIG_TEXT: [error] 27895#0: *5468586 upstream sent too big header while reading response header from upstream

Product issue:

#PPPM-11672 "Retrieving keys now works correctly (a 502 Bad Gateway error is no longer shown) on servers with a large number of customers, resellers, or additional users (more than 700)."
Fixed in:
- Plesk Obsidian 17 March 2020

Please consider updating your server:

As a workaround:

Plesk running on Windows

Connect to the server via RDP.
Download WebsiteList.php.
Create backup of %plesk_dir%admin/plib/ServerInfo/WebsiteList.php and replace it wirh downloaded WebsiteList.php.
Retrieve key in Tools & Settings > License Management.

Plesk running on Linux

Connect to the server via SSH.
Open the file /etc/sw-cp-server/config and change the following parameters as below:

CONFIG_TEXT: fastcgi_buffers 64 128k;
fastcgi_buffer_size 128k;
Restart sw-cp-server and sw-engine services:

# service sw-cp-server restart && service sw-engine restart
Retrieve key in Tools & Settings > License Management.

If steps above did not help, run:

# plesk bin license --retrieve