Why does ProxyPass return 503?

Question

Apache HTTP Server

Hello! I have a goal to upload an ASP.Net Core Web API project to an Ubuntu 20.04 server. I am a beginner developer, used this manual
Here is my /etc/apache2/sites-available/api.conf :

<VirtualHost *:*>
    RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
</VirtualHost>
<VirtualHost *:80>
    ProxyPreserveHost On
    ProxyPass / http://127.0.0.1:5000/ retry=0
    ProxyPassReverse / http://127.0.0.1:5000/
    ServerName 80.249.146.56
    ServerAlias www.80.249.146.56
    ErrorLog ${APACHE_LOG_DIR}api-error.log
    CustomLog ${APACHE_LOG_DIR}api-access.log common
</VirtualHost>

The 503 Service Unavailable error occurs at the ProxyPass location, without this the Apache server starts up and runs fine. SELinux is disabled. retry=0 added. I don't know what to do anymore.

Answer 1

Does the error mean that there is nothing on 127.0.0.1:5000
netstat -ltpndthat says anything?