There is limitation in nRF UART app. I can only sent 20 character at a time. I need to send more than 20 character because I am inter face with my energy meter. It is following DLMS protocol.
The effective payload packet may be limited to 20 bytes if you use an old phone that doesn't support long MTU. I'm not familiar with this protocol, but I imagine you can split and reassemble the packets in your app and FW.
