Steps to reproduce:

1. create host with user macro with some value, like {$TESTING} with value: f077bfbe-50b9-48e6-97b0-b815c3adb353
2. create zabbix trapper item to that host, like testing[\{$TESTING}]
3. send using zabbix_sender/zabbix_utils data to that host/item

Result:
Data isnt received to item

Expected:
Data is received

If item is created as testing[f077bfbe-50b9-48e6-97b0-b815c3adb353] then data is received.

Documentation states that usermacros can be used in item-keys.