This reference is derived from the 1.8.x filter grammar.
Verify, you are using the right version of nfdump: Version needs to be 1.8.0 at least.
% nfdump -V
nfdump: Version: 1.8.0-d87b550f options: lz4 ZSTD CRYPTO PCRE2 JA4 read-pcap date: 2026-10-06 18:25:16 +0200