The REST Library in Delphi Rio has a serious error. I was last weekend at the world's largest HackYeah hackathon, where I needed to use the Delphi Rio to connect to the rest service. However, I could not. REST Debbuger did not return any error or response after calling the request (button Send Request). I lost a lot of time on the verification of network connections and the operation of the server itself (I thought that a heavy load on the hackatone participants "killed" the server) but it turned out to be a mistake in the REST Library. When I tried to call the request directly from Delphi (request.Execute ()) I got an error in KERNELBASE. There is no error in Delphi Tokyo, the same code worked there, but on my laptop I only had Rio. So I was looking for a solution. Eventually, I found the place and the reason, corrected RTL file (after copy to project directory) and the code runed, but the bad taste remained. Later I will publish where the error lies.