test configuration :

template1 -> template2 -> host

in host agent :
UserParameter=macro[*],echo '$1' > /tmp/macro.txt; echo 1
UnsafeUserParameters=1

in template1 (only !) : user macro "{$MACRO}"

create agent item (both active and passive fail) with key "macro[{$MACRO}]" (frontend resolves this properly if $1 is used in description).

on host, {$MACRO} is written to the debug.

works fine if usermacro is defined on template2