Hello mbed community .
i try to use Gsm library for A9 GSM ai thinker module with Nucleo F103RB but i have a problem of " unknown Serial type" in online compiler
please i need your help


That Is probably caused by MbedOs version in your project. MbedOs < 6 has Serial API, but in MbedOs6+ was splited into two APIs - BufferedSerial and UnbufferedSerial API.
So you need to downgrade MbedOS to 5.15.8 or Update your library for MbedOS6+

Usually is good to share library what you are trying to use via link.

And that Mbed OS Tech Forum - Live Stream - #44 by Koki123 is off-topic for this thema.

BR, Jan