Installing ddns-scripts: Parse error (invalid command)?

Okay, I've tried again and provided/selected the following settings for a no-ip.com account copy-pasting from a plaintext editor:

Lookup Hostname: MySubdomain.ddns.net
IP address version: IPv4-Address
DDNS Service provider [IPv4]: no-ip.com
Domain: MySubdomain.ddns.net
Username: MyNoIPAccount
Password: MyNoIPAccountPassword (something like bc9d0faad5a84989a896aj72da2f4763)

...and still get the error (my current ISP router uses the credentials without problems).

But honestly I don't understand the "Lookup Hostname" field. I don't get what https://wiki.openwrt.org/doc/howto/ddns.client wants me to provide here. Chapter "Configuration" -> "Basics" says:

Host/Domain: your FQDN you want to update (used by ddns-scripts using nslookup to check if update has happen)

and

Lookup Host: ONE of your defined FQDN you want to update (used by ddns-scripts using nslookup to check if update has happen)

The example text in LuCI (myhost.example.com) suggests (in my perspective) to provide the dynamic DNS domain here, so MySubdomain.ddns.net. Is this right? Doesn't make sense somehow.