USG FLEX 50 log format for a Synology log server

Hi !

I'm trying to send my USG FLEX 50 logs to a Synology log server but I'm struggling with the format.

Both "Syslog" and "CEF/Syslog" appear to not be supported by Synology, as values are not mapped properly.

There is, in the Synology log server settings, an option for a custom format using a pattern parser (for example @STRING:Hostname:@), but I cannot seem to find how to make it work, despite having used pretty much anything I could find in the syslog-ng documentation (linked in the Synology logs docs)

Has someone successfully sent their USG FLEX logs to a Synology NAS in a usable form ?

Thanks.