Craft 3: 500 Internal Server Error when trying to install on server
The 503 error on the home page usually indicates that Craft can't connect to the database. That's to be expected when performing a fresh installation.

The internal server error could be a typo or other misconfiguration in the /web/.htaccess file. You can troubleshoot this by renaming the .htaccess file so Apache doesn't use it, then in /config/general.php set

'omitScriptNameInUrls' =&gt; false,


index.php?p=admin should work then and you can sort out the .htaccess url rewrites later.