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Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 21.0.7): 21.0.7
Operating system and version (eg, Ubuntu 20.04): Arch linux
Apache or nginx version (eg, Apache 2.4.25): 1.19.7
PHP version (eg, 7.4): 8.0.2
The issue you are facing:
I can’t open the files app. I receive a Bad Gateway 502 Error
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
- open files app in Browser
The output of your Nextcloud log in Admin > Logging:
{"reqId":"4YN7kFK8MYS5NUkmor9a","level":0,"time":"2021-02-24T14:30:26+00:00","remoteAddr":"xxx","user":"max","app":"scss_cacher","method":"GET","url":"/apps/files/","message":"SCSSCacher::process ordinary check follows","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0","version":"21.0.0.18"}
{"reqId":"4YN7kFK8MYS5NUkmor9a","level":0,"time":"2021-02-24T14:30:26+00:00","remoteAddr":"xxx","user":"max","app":"scss_cacher","method":"GET","url":"/apps/files/","message":"SCSSCacher::isCached 6328-74d9-merged.css isCachedCache is expired or unset","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0","version":"21.0.0.18"}
{"reqId":"4YN7kFK8MYS5NUkmor9a","level":0,"time":"2021-02-24T14:30:26+00:00","remoteAddr":"xxx","user":"max","app":"scss_cacher","method":"GET","url":"/apps/files/","message":"SCSSCacher::isCached NotFoundException /appdata_ocmyl63yjxna/css/files/6328-74d9-merged.css","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0","version":"21.0.0.18"}
{"reqId":"4YN7kFK8MYS5NUkmor9a","level":0,"time":"2021-02-24T14:30:26+00:00","remoteAddr":"xxx","user":"max","app":"scss_cacher","method":"GET","url":"/apps/files/","message":"SCSSCacher::process Lock acquired for /wapps/files/css/merged.scss","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0","version":"21.0.0.18"}
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
PASTE HERE
The output of your Apache/nginx/system log in /var/log/____:
PASTE HERE