Defining custom feature codes

I’m trying to create a new in-call feature code, to use for extending conference features (planned to become a ‘pull-external-numbers-into-confbridge’ feature), but I can’t seem to get it to activate.
The standard in-call feature codes like ## for transfer or *1 for one-touch-record are working, so DTMF is correctly recognized.
I tried assigning *33 to my feature, using an example from the wiki, by adding
apptestfeature => *33,peer/both,Playback,tt-monkeys
to features_general_custom.conf
When I do ‘features reload’ and ‘features show’ in the Asterisk console, I correctly see
== Registered Feature 'apptestfeature' == Mapping Feature 'apptestfeature' to app 'Playback(tt-monkeys)' with code '*33' Dynamic Feature Default Current apptestfeature no def *33 apprecord no def *1
but while *1 works, *33 does not. Neither does it show up on the Asterisk console nor the full logfile. The feature code plainly seems to be ignored.

Any ideas on how to get this to work?

(infrastructure in use: FreePBX on Asterisk 11.8.1, clients being tested with: Grandstream GXP2140, CSipSimple, MicroSIP, Zoiper)

… and as soon as I post here, the solution becomes obvious: I missed the
in globals_custom.conf

This at least makes it work during a normal 1:1 call. I still need to figure out, though, how to make feature codes work from within a conference. Any hints on that?