That's because your Blitz installation doesn't include the Lotan DOS library (and the Elmore libraries containing the Request() function). It looks like you're using the default installation - I think the documentation gives details on adding libraries to the setup, but it involves using a tool to add them to the "deflibs" file that contains all the commands Blitz can use. I vaguely remember there also being a way of adding libraries to a folder to add individually, but I can't remember the details... Anyway, check the documentation - the basic installation is intended for floppy-only use (and the BlitzISOToFloppy tool simply recreates the floppies from the files on the CD). As such, it's very minimal and contains only the most basic components.
If you check the Extras drawer, you should find files with updated components, such as a bigger deflibs file that I think will contain the commands you need, a better debugger and so on. Try the bigger deflibs file anyway, see how that goes. Using Include is for including other Blitz source files, not command libraries which are loaded by Blitz when it starts, and can't be loaded by your code.
As an aside, is there a reason you're using OS 1.3? Using OS 2+ allows you to use a much nicer editor, AmigaGuide documentation and so on. Additionally, there's a [
http://ubb.plus/]revised version of the Blitz CD ISO[/url] which includes all the latest updates as well as a fixed installer, but you really need OS 2 to get the most from it.