Alexa control of an MQTT cover - CLOSE command not supported?

Hello. I’ve searched the forums here and found some similar topics, but nothing exactly like this, and no solution which helped me.

I’m using a Sonoff SV, modified to work as a dry contact (removed the two resistors), to command a motorized gate. All of the config data appears below. Electrically, everything works fine between the Sonoff and the gate controller.

Also, the open and close commands, plus the state changes from the reed switch, all work fine under HA.

The problem I have is when trying to use Alexa to control the gate. The OPEN command works just fine. When I tell Alexa to CLOSE the gate, it replies that the command is not supported. Very strange that one, and not the other, command would be supported. If it matters, I’m using Alexa via NabuCasa.

Additional info, I also have a Somfy shade which is integrated via the Tahoma box (this is also a cover). The OPEN and CLOSE commands (via Alexa) both work fine with this cover.

Anyone have any ideas how to fix this? Thanks!

Here’s my configuration.yaml:

  - platform: mqtt
    name: "portail"
    state_topic: "cmnd/gatestate/POWER2"
    command_topic: "cmnd/SonoffPortail/POWER"
    payload_open: "ON"
    payload_close: "ON"
    payload_stop: "ON"
    state_open: "OFF"
    state_closed: "ON"
    optimistic: false
    retain: false
    unique_id: driveway.gate *(I added this to get around the "no unique id" message from HA)*

here’s my customize.yaml:

  device_class: gate
  friendly_name: Portail 

Mmm… Same payload for open and close?

Yes, because the gate control unit requires a single pulse (closed contact, for about a second) for open, close, and stop orders. It’s a pretty old system, no feedback or anything else fancy.
I’ve got a reed switch to tell me when the gate is open or closed (the gatestate item in the mqtt definitions)