How to use preprocessing with Discovery rules?

[nameuser]

Zabbix 4.0.4

I made a host with some discovery rules. But zabbix-agent send to server invalid JSON.
More precisely, JSON have 2 extra numbers before JSON's default

{"

For example, input JSON seems like this:

18
{"data":[{"{#SCOPEID}":"10.46.1.0"},{"{#SCOPEID}":"10.46.3.0"},{"{#SCOPEID}":"10.46.16.0"},{"{#SCOPEID}":"10.46.17.0"},{"{#SCOPEID}":"10.46.18.0"},{"{#SCOPEID}":"10.46.19.0"},{"{#SCOPEID}":"10.46.20.0"},{"{#SCOPEID}":"10.46.21.0"},{"{#SCOPEID}":"10.46.22.0"},{"{#SCOPEID}":"10.46.23.0"},{"{#SCOPEID}":"10.46.32.0"},{"{#SCOPEID}":"10.46.33.0"},{"{#SCOPEID}":"10.46.34.0"},{"{#SCOPEID}":"10.46.38.0"},{"{#SCOPEID}":"10.46.41.0"},{"{#SCOPEID}":"10.46.44.128"},{"{#SCOPEID}":"10.46.47.0"},{"{#SCOPEID}":"192.168.37.0"}]}

I know how to use Item preprocessing, for example, trim function. But I can't figure out how to trim my discovery rule, because it has no Preprocessing tab

I can't do anything with this zabbix-agent, because it's totally not up to me, so please don't tell me to fix JSON output.
The only thing I can do - is to trim JSON input, but I don't know how