How to resolve An unknown error has occurred while uploading files to Nextcloud?

I faced problem like below when I upload file.
An unknown error has occurred

Conclusion is HTTP 413 Request Entity Too Large happened in my environment.

I expanded upload limit size to 128MB.

First is https-portal which acts as reverse proxy.
You only need to insert this line.

CUSTOM_NGINX_YASUFUMI_YOKOYAMA_GQ_CONFIG_BLOCK: 'client_max_body_size 128M;'

Next is configuraiton of Nginx.
You need to add this line to server block.

client_max_body_size 128M;

After editing them, you need to restart each Nginx!

Conclusion

How was it?

You can do it in 5 mins!