ChirpStack - Dragino - EndNode: Downlink issues

Hello Community,

For starters, I have a Chirpstack server running on an instance of Ubuntu. It runs perfectly, I managed to add my Dragino Gateway and controller .
For the Gateway part, I chose “LoRaWAN–Semtech UDP”. In the “Primary LoRaWAN Server” section I chose as follows: “Service Provider” → “Custom/Private LoRaWAN”, “Server Address” → “My ChirpStack server ip : port”. As I said above, it connected and works perfectly, managing to uplink from End-Node to ChirpStack via Gateway successfully.

The problem I encountered and am asking for help with is on the Downlink side. I found the downlink section in the Chirpstack server, called “Enqueue downlink payload”, where I selected the port, confirmed the donwlink, and in the “Base64 encoded string” section I entered the message: “Gg==” because after encoding I want my controller to receive the message “1A”. I managed to downlink once, after that whenever I wanted to downlink it didn’t work, regardless of the port or the message I wanted to send.

Later on, I managed to point the Dragino Gateway to a TTN instance, to try and with this platform to do uplink and downlink with the same Gateway and the same Controller. In this configuration: “End-Node → Dragino(Gateway) → TTN” worked perfectly and I was able to uplink and downlink.
Could you help me with a tip why I fail to downlink in the configuration “End-Node → Dragino(Gateway) → ChirpStack” ?

The photo is too blurred. I can not see any details.
Seem the Arduino nodes can receive something on the console.

BTW, my Dragino gateways and nodes work well for uplink and downlink from Chirpstack v3 and v4.