So, APIs generally just return data. That's probably their smartest use-case. You build a website and then have something that queries an API to do the actual number crunching and then that website displays the result.

You can have an APIFunction return something more complicated like a webpage, or in this case, something as complicated as a CDF document. CDF is the WolframLanguage's web format for interactive documents:

CloudDeploy[
 APIFunction[{"yVar" -> "Number"}, 
  ExportForm[plotSineFunction[#yVar], "CloudCDF"] &], "spAPI"]

There was a request for clarification so let me try to provide that here...

We are logging events from multiple devices located in multiple sites into a databin. As part of this logging we are capturing the site from which the log event is made by adding a site ID (sID) to the event; my original post said system ID but a more accurate description would be site ID. All of this is working fine.

This done we began developing code using the Wolfram Development Platform that accesses the databin and uses the sID to create a site-specific dataset; it basically extracts site-specific events from a databin that contains events from multiple sites. This site-specific dataset is then used to generate site-specific stats. All of this too is working fine but at present the sID is hard-coded...

sID="Site01"

The problem is that we have to change the code every time we want to show a different site; for example...

sID="Site02"

Etc.

Ideally, we'd like to pass the sID in a URL that calls our code; for example...

https://www.wolframcloud.com/objects/879e8689-dddf-4e33-a908-37773e9f73df?sID="Site03"

This would enable us to support multiple sites from one code base rather than having to customize the code with hard-coded sID for each site.

Hope this provides the clarification requested.

Good code is broke up into reasonable sized functions, each of which performs a coherent task.

I'm not sure what your background is with programming, but knowing how to make functions is important. I'll try to keep this definition flexible and simple.

To create a function use the following syntax:

(* Comment saying what "myFunction" does *)
myFunction[argument1_, argument2_,argument3_] :=
    Module[{},
        something;
        something;
        something;
        (* The value to be returned by the function is the last value and doesn't have a semicolon after it *)
          valueToBeReturned
    ];

As an aside, the first argument to Module shown here is an empty list. You can put the names of variables in that list and those variables will be localized to the Module. Localizing variables is a good idea, if you're familiar with the concept. Otherwise, this is the general idea of how you make a function in the Wolfram Language.

I think I have a simple example to explain what I'm trying to do...

y=1;
Manipulate[Plot[Sin[x (y + a x)], {x, 0, 6}], {a, 0, 2}]

Assume this is my entire code. I set the value of y and call a Manipulate function which in turn draws a sine plot that can be manipulated over x. Is it possible to create a Cloud Deploy URL that passes y as a URL variable and ends up drawing the associated sine plot?