invalid peer certificate contents: invalid peer certificate: UnknownIssuer

Hi,

Set-up is done and correct according to the setup utility, unfortunately when I test with the test_client program I have an error.
Here is my config, followed by the error.
Config

[Unit]
Description = Push daemon for Nextcloud clients

[Service]
Environment=PORT=7867
Environment=NEXTCLOUD_URL=https://nextcloud.xxxxxx.com
Environment=ALLOW_SELF_SIGNED=true
ExecStart=/var/www/nextcloud/apps/notify_push/bin/x86_64/notify_push /var/www/nextcloud/config/config.php
User=www-data

[Install]
WantedBy = multi-user.target

nextcloud.xxxxxx.com is added to my /etc/hosts as 127.0.1.1 nextcloud.xxxxx.com

error

nextcloud@nextcloud:~# ./test_client http://nextcloud.xxxx.com YYYYYY YYYYYYY
[2022-07-25 00:34:41.359171 +02:00] WARN [rustls::conn] /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/rustls-0.20.2/src/conn.rs:1197: Sending fatal alert BadCertificate
Error:
  x http://nextcloud.xxxxx.com/ocs/v2.php/cloud/capabilities: Connection Failed: tls connection init failed: invalid peer certificate contents: invalid peer certificate: UnknownIssuer
  `-> invalid peer certificate contents: invalid peer certificate: UnknownIssuer

Thank you very much !

Start by reproducing the failure with the mentioned test_client program and the supplied service configuration, focusing on the rustls UnknownIssuer error. Check how ALLOW_SELF_SIGNED=true is handled and compare it with the certificate and host setup described in the issue; done means the certificate-handling cause and expected behavior are established.