Serial monitor showing extra data
char reqst[] = " ";


Here you created an array two chars in length. But one of those characters must be used for the null terminator so actually it can only hold a string that's a single character long. If you write past the end of the array that will cause undefined behavior. This is likely to be the cause of the strange results you encountered. You need to size reqst[] large enough to contain any string you may receive, including the null terminator. You should add code to ensure that you never write off the end of the array and that it will always end in a null terminator.

I realize it may only be a simplified minimal example, but in the code you posted there is no need to store the incoming characters. Instead you could just print them as they are received.