Apache Proxy Error (502)

General
1

I installed gitea 1.7.6 on Unbuntu 18.04 LTS with Apache 2.4.26 and Mysql.
When app.ini configuration had PROTOCOL = https I an into Problems with letsencrypt
[E] Failed to load https cert file localhost:3000: open /etc/letsencrypt/live/git.arbyte.net/fullchain.pem: permission denied

So I went for the solution provided here and set PROTOCOL = http.
This is my configuration in app.ini:

[server]
PROTOCOL         = http
ROOT_URL         = https://my.domain.tld/
SSH_DOMAIN       = my.domain.tld
DOMAIN           = my.domain.tld
HTTP_PORT        = 3000
HTTP_ADDR        = localhost
DISABLE_SSH      = false
SSH_PORT         = 22
LFS_START_SERVER = true
LFS_CONTENT_PATH = /var/lib/gitea/LFS

Service is running now but doing so gives me this in the Browser:

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET / .

Reason: Error reading from remote server

and apache’s error.log:

[proxy_http:error] [pid 28572] (103)Software caused connection abort: [client 84.113.179.56:51972] AH01102: error reading status line from remote server localhost:3000
[proxy:error] [pid 28572] [client 84.113.179.56:51972] AH00898: Error reading from remote server returned by /
[proxy_http:error] [pid 28572] (103)Software caused connection abort: [client 84.113.179.56:51972] AH01102: error reading status line from remote server localhost:3000, referer: https://my.domain.tld/
[proxy_http:error] [pid 28571] (103)Software caused connection abort: [client 84.113.179.56:51973] AH01102: error reading status line from remote server localhost:3000, referer: https://my.domain.tld/
[proxy:error] [pid 28571] [client 84.113.179.56:51973] AH00898: Error reading from remote server returned by /favicon.ico, referer: https://my.domain.tld/
[proxy_http:error] [pid 28571] (103)Software caused connection abort: [client 84.113.179.56:51973] AH01102: error reading status line from remote server localhost:3000, referer: https://my.domain.tld/s$
[proxy_http:error] [pid 28568] (103)Software caused connection abort: [client 84.113.179.56:51974] AH01102: error reading status line from remote server localhost:3000, referer: https://my.domain.tld/s$
[proxy:error] [pid 28568] [client 84.113.179.56:51974] AH00898: Error reading from remote server returned by /serviceworker.js, referer: https://my.domain.tld/serviceworker.js

Any Ideas?

[EDIT]
my apache configuration:

<IfModule mod_ssl.c>
<VirtualHost *:443>
    ServerAdmin XXXXX
    SSLEngine on
    SSLProxyEngine on
    SSLProxyVerify none
    SSLProxyCheckPeerCN off
    SSLProxyCheckPeerName off
    SSLProxyCheckPeerExpire off
    ProxyPassReverseCookieDomain localhost my.domain.tld
    ServerName my.domain.tld
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined

    SSLCertificateFile /etc/letsencrypt/live/my.domain.tld/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/my.domain.tld/privkey.pem
    Include /etc/letsencrypt/options-ssl-apache.conf


    ProxyPreserveHost On
    ProxyRequests off
    ProxyPass / https://localhost:3000/
    ProxyPassReverse / https://localhost:3000/
</VirtualHost>
</IfModule>