Cannot connect to Transmission running as Synology package, but can using same settings with transgui

[lilygthb]

Using Transmission Remote GUI I can successfully connect to Transmission running on a Synology, not in Docker, but as a Synocommunity Package. I'm using these setting to connect:

I can't connect using TrguiNG , I'm using these settings:

Which to me look the same settings used by transgui, but I get this error:

Is there something I'm missing?

[lilygthb]

I made it work using these settings:

[qu1ck]

Yeah TrguiNG is asking specifically for RPC url which ends with /rpc.
The hint in the field (visible when it's empty) also shows this.