Getting an error while trying to connect custom Board based STM32L4 Series Chipset

Hi, I just want to build model for my custom board stm32l431rct6 via stm32f303vct6 discovery board, So Iniatially I faced lot of struggles, so I ve decided to build a model for only Disco board, I can able to build, deploy and run the model and also can able to do monitor and run the model via vcp protocol( this is the main concern which I am facing rn ). I can do this in disco board....In custom as far as in STM32L4 Series Uart2 is the standard one for the vcp protocol so tapped the wire directly from it which is connected to JP4 pins in STLINK Disco board for the protocol...so Iniatially I can able to build, deploy and run the basic model in custom board but I cant able to do the same thing in Monitor and run mode and Im getting the this error.