Hi, I downloaded Serial Bluetooth Terminall APP and managed to go to Custom LE profile, but cannot figure out how to give those UUIDs. It is not possible to write anything to service UUID, if I click it, app tries to connect, but fails.
It appears that I have the same problem as you. You can send configuration commands (TTM) via Bluetooth, but trying to send something from MCU (I have Seeduino XIAO) via TX,RX fails.
I think someone in Seeedstudio should explain what is the problem here