The flag is : The valid serial number
file: RM.exe: PE32 executable (GUI) Intel 80386, for MS Windows
When we launch the binary, we are asked an email and a serial number.
We jump into IDA and watch the decompiled functions, we quickly find an interesting one DialogFunc, this function handle the click event on the validation.
We can clearly see that the program just verify if the input in the email field is valid and then check some hardcoded registration serial, we just get the values, put them in order and valid the program with the serial: CZ9dmq4c8g9G7bAX
The flag is: CZ9dmq4c8g9G7bAX