Confirm Genuine or Fake Bluepill Board

There are several possibilities, which have been discussed several times here in the community. Nevertheless, you can safely assume that there is a fake on a Blue Pill. This has also been discussed at length on Hackaday, and they have also created a diagnostic program that should be able to detect such fakes.

If you absolutely want to keep the board, you should consider desoldering the fake MCU and soldering on a real STM32F103. However, the best and less expensive alternative is to forget all this fake stuff and buy a NUCLEO board, because it is ultimately cheaper.

Hope that helps.

Good luck!
/Peter

And what do you exactly mean by "is not functioning as expected" ?

Many of BluePills use Chinese STM32F103-alikes. Some of them are 99.9% compatible, some only 98% compatible, but they do their work. It's just that genuine ST software and hardware tries very hard to avoid supporting them. You may encounter problems with debugging, as ST refuses to connect to the non-genuine stuff (and that's quite ok - why should they provide development support for alien and not quite legally ok chips?). Once you have your firmware verified on a real STM32F103 and programmed into the clone via UART bootloader, it works.