Configurable length of the source NAT pool name, destination NAT pool name, source NAT rule name, destination NAT rule name, static NAT rule name, and rule set name characters limitation.

root@> show version 

Model: srx4600

Junos: 20.3R3.8

root# set security nat source pool reflect_CORE_OMCH_ukdlhc00026do-SNA

                     ^

Length 35 is not within range (1..31) at 'reflect_CORE_OMCH_ukdlhc00026do-SNA'

Starting in Junos OS Release 21.4R1 the configurable length of the source NAT pool name, destination NAT pool name, source NAT rule name, destination NAT rule name, static NAT rule name, and rule set name from 31 characters to 63 characters.

https://www.juniper.net/documentation/us/en/software/junos/release-notes/21.4/junos-release-notes-21.4r3/junos-release-notes-21.4r1/topics/new-features/feature-descriptions/nat-4.html