I actually had this just happen a few minutes ago. Did the same thing, heard the audio clip play saying the supply drop had been requested and then nothing. I retried previewing the custom mission three times, and on the third time I tried requesting the supply drop, it locked the game.

maybe because its an alpha......

Maybe. Although why it would, in my case, lock up the game is a bit of a mystery then. Also since most of the other support modules do work, it is somewhat reasonable to bring this one not working to their attention.

If they didn't activate the module yet, then I'm sure the dev team will clear this in about 10 seconds. If not, now they know there might be a problem with it.

Support modules Drop ammo in beta gives two options

1. Virtual

a chopper appears says drop completed then vanishes.

2. If requesting a chopper from a ground location to drop nothing happens.

3. If requesting a pickup up same thing except virtual sometimes the chopper hovers allowing a pickup.

Have also noted that the option to request sometimes vanishes altogether after 1 request.

Supply drop with preplaced aerial unit worked for me in ArmA 3 1.00

However I did not test the virtual ammo drop yet.

Supply Drop works in the Editor BUT nothing is dropped in mission on a dedicated Server. This is an old problem that was fixed once before. Reoccurred after APEX update. Virtual supply request works; as in Helicopter arrives but no crate is dropped.

@jgaz-uk
I tried basic setup for the Supply Drop request and everything seems to work fine, both in editor and on dedicated server.
Would you mind uploading a repro of a mission where you are trying to request the drop and nothing happens?