LAMP stack install issues in step 3: Primary script unknown

[rinorway]

Looking for a fast Testserver, I ended up at Vultr.com, starting from 5 eur/month.


So I selected : LAMP stack

• deployed (Ubuntu 2204 LTS, PHP/FPM 8.2, MariaDB )
• got certbot cert
• created db + espouser
• a2enmod rewrite
• unpacked the last release and started /install

All fine and in a breeze.

But at step 3 in the install, the "test connection" XHR :

POST https://myhost.com/install/index.php

gives a 404 error :

[proxy_fcgi:error] [pid ..:tid ...] [client ..] AH01071: Got error 'Primary script unknown', referer: https://myhost.com/install/

The body is ok :

​dbName=mydb&hostName=localhost&dbUserName=myuser&dbUserPass=myspass&action=settingsTest
​

If I post the same body to

POST https://myhost.com/install/

so without the index.php rewrite, the result is a nice http 200

{"success":true,"errors":[]}

FCGI debugging is a pain, and I tried about anything ( all stackexchange and serverfault suggestions)

My question : what is the best way to tackle this? Why does this only happen at step 3 in the install process?

Thank you for thinking along