Portainer: Client sent an HTTP request to an HTTPS server – despite the URL is https:// – Docker

I am pretty new for the topic server configuration and now I got a problem with to reach a container with ssl certificate.

What is my setup:

I’ve got a raspberry pi with docker on it. The container which is connected to port 80 and 443 is a reverse proxy which is directing incoming subdomains to different other container.
Example:
webserver.my-domain.com is leading to IP 192.168.178.69:8080. I archived this through this config in the folder sites-enabled:

<VirtualHost *:80>
 ServerName webserver.my-domain.com
 ProxyPreserveHost On 
 DocumentRoot /var/www/html
 ProxyPass /.well-known !
 ProxyPass / http://192.168.178.69:8080/
 ProxyPassReverse / http://192.168.178.69:8080/
RewriteEngine on
RewriteCond %{SERVER_NAME} =webserver.my-domain.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

I also created a let’s encrypt certificate inside of the reverse proxy container. This created an additional file webserver-le-ssl.conf:

<IfModule mod_ssl.c>
<VirtualHost *:443>
 ServerName webserver.my-domain.com
 ProxyPreserveHost On 
 DocumentRoot /var/www/html
 ProxyPass /.well-known !
 ProxyPass / http://192.168.178.69:8080/
 ProxyPassReverse / http://192.168.178.69:8080/

SSLCertificateFile /etc/letsencrypt/live/my-domain.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/my-domain.com/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
</VirtualHost>
</IfModule>

So far so good. My content is available if I try the URL https://webserver.my-domain.com.

What is my Problem

I use Portainer to manage my docker container and I want Portainer to be available through portainer.my-domain.com.
So this is the portainer config inside of sites-enabled:

<VirtualHost *:80>
 ServerName portainer.my-domain.com
 ProxyPreserveHost On 
 DocumentRoot /var/www/html
 ProxyPass /.well-known !
 ProxyPass / http://192.168.178.69:9443/
 ProxyPassReverse / http://192.168.178.69:9443/
RewriteEngine on
RewriteCond %{SERVER_NAME} =portainer.my-domain.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

And also the ssl config for this:

<IfModule mod_ssl.c>
<VirtualHost *:443>
 ServerName portainer.my-domain.com
 ProxyPreserveHost On 
 DocumentRoot /var/www/html
 ProxyPass /.well-known !
 ProxyPass / http://192.168.178.69:9443/
 ProxyPassReverse / http://192.168.178.69:9443/

SSLCertificateFile /etc/letsencrypt/live/my-domain.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/my-domain.com/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
</VirtualHost>
</IfModule>

If I call 192.168.178.69:9443/ I can reach the container without problems.
But if I try to reach the URL portainer.my-domain.com I just got the Message:

Client sent an HTTP request to an HTTPS server.

But in the URL shows: https://portainer.my-domain.com/.
So I don’t understand why there is an HTTP request, even if my browser shows me that the connection is with https.

Can someone explain this to me and show me how to fix this?

Update: My solution
With a lot of tries I found a solution:
As I run the reverse proxy and the portainer as docker containers, I put both containers into a network with docker-compose:

version: "3.4"

services:
  apache:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - /home/pi/reverse-proxy/:/etc/apache2
    networks:
      - homeserver

  portainer:
    image: portainer/portainer-ce:latest
    ports:
      - "8000:8000"
      - "9000:9000"
      - "9443:9443"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - portainer_data:/data
    networks:
      - homeserver

networks:
  homeserver:

volumes:
  portainer_data:

The volume of the apache2 is the complete config folder of /etc/apache2. After that I changed the IP of the ProxyPass to the name of the container:

 ProxyPass / http://reverse-proxy_portainer_1:9000/
 ProxyPassReverse / http://reverse-proxy_portainer_1:9000/

After this changes it worked.