ENOTFOUND message at config Sync on Mac OS

Operating system

macOS

Joplin version

3.5.13

Desktop version info

Joplin 3.5.13 (prod, darwin)

Gerät: darwin, Apple M1
Client-ID: 8d8d04bfbed54c1b99a918a5260cd32c
Sync-Version: 3
Profil-Version: 49
Unterstützter Schlüsselbund: Ja
Alternative Instanz ID: -

Revision: 0c1511f

Backup: 1.5.1
Freehand Drawing: 4.2.0

Sync target

Joplin Server

What issue do you have?

Hello,

When I try to set up synchronization with the server running on my Synology, I get the following error message:
"request to https://joplin.su-behning.de/api/sessions failed, reason: getaddrinfo ENOTFOUND joplin.su-behning.de (Code ENOTFOUND)"

Sync works on my iOS devices.
It also used to work on my Mac. I have since switched to my own (sub)domain with an SSL certificate. However, I can’t say for sure whether the error message is related to the switch, but it’s certainly possible.
The address points to Pi-hole, from there it goes to the NAS’s reverse proxy. The traffic runs through Tailscale; the “su-behning(dot)de” domain is redirected via CNAME to the Tailscale IP at the provider to enable VPN access.
Previously, the Mac had no issues while iOS was having problems; now it’s the other way around.

Does anyone have any ideas?
Thanks & regards,
Ulrich