Nginx reverse proxy configuration for OnlyOffice

I am here: Configure Nginx for OnlyOffice.

But after then I receive a 502 Bad Gateway from Nginx when I call: http://seafile.mydomain.tld/onlyofficeds/welcome.

I can call onlyoffice at: http://seafile.mydomain.tld:88/welcome.

What’s the problem with nginx configuration? For test cases I work with HTTP, to not have certificates.