When a macro is used in the key of a trapper item, the server will only accept data if you specify the key with unresolved macro names.

eg:
host "host01" has a trapper item "trapperdata[{HOST.NAME}]"

zabbix_sender [...] -k "trapperdata[host01]" [...] FAIL
zabbix_sender [...] -k "trapperdata[{HOST.NAME}]" [...] SUCCESS