How to do WriteNoResponse with NimBLE server

[freeride01]

Hi,
I'm trying to set up a "write-no-response-only" characteristic on a NimBLE server.
I can successfully write to it with a "normal" write request and the gatt_svr_chr_write function.
For write-no-response, I set the BLE_GATT_CHR_F_WRITE_NO_RSP flag and substitute the above function with ble_gattc_write_no_rsp (it' gattc, but it's under "GATT server reference" in the NimBLE user guide, so I figured I'd try it).
The problem is, I get nothing written to my buffer.
Is there something else that has to be done on the server side for write-no-response to work?
Thanks.