Stuck installing on Debian 10: 502 Bad Gateway error when trying to get to install.php

Hi thank you for chiming in,

Got this OK

yes.

default debian (well, the ‘+backports’ from minimal ‘netinstall’ dvd image). So no firewall by default.

I have, but I did it at first as the docs said -
(https://docs.librenms.org/Installation/Install-LibreNMS/) - it ended with ‘502 Bad Gateway’ error when i went to ‘install.php’ stage;

then I googled and tried doing it more ‘debian’ way
(https://computingforgeeks.com/install-and-configure-librenms-on-debian-with-nginx/) whence at least one discrepancy came from (the docs have /run/ path to socket, the other instructions way has /var/run path to socket;)

then I tried making it good either way (/var/run in both php-fpm and nginx config, then /run in both) and still it did not help - other than changing from ‘file not found’ to permission denied’ in the error.log;

(that above suggestion came from Unable to continue fresh install - http://SERVER_IP/install.php giving 502 Bad Gateway - #4 by Barton)

And as of now, it’s still not working…
the

/var/log/nginx/error.log

says
connect() to unix:/run/php/php7.3-fpm-librenms.sock failed (13: Permission denied)…

And of course the 502 error still persists…

Which permissions is it missing and what should they be?