FortiOS 7.2.4 Unable to use DynDNS Name for IPSec Remote Gateway

Struggeling at a customers Firewall, which is running at FortiOS 7.2.4 (please no bashing, I know...).
It's quiet not possible to set the FQDN for DynDNS Gateway in IPSec Phase1 and an error message (-9999: -9999) pops up. No change possible. The CLI parameter (following the reference guide) is not implemented yet (Parse error before "remotegw-ddns"...).

Is anybody else struggling on these? Any solution or workaround?