Use custom resources.

Should be

  If glo["ABC",type="K" Set restmode=0           /*except if a kill on ^ABC*/ 

Instead of

  If glo["^ABC",type="K" Set restmode=0           /*except if a kill on ^ABC*/ 

Globals can't have duplicate keys.

After I execute your code and call

zw ^Data 

I get this output:

^Data("Athens")=7
^Data("Boston")=3
^Data("Cambridge")=1
^Data("London")=4
^Data("New York")=2

Please post CROSRestAPI as text.

Can you get InterSystems IRIS or a complete version of Cache/Ensemble?

Service Unavailable error is because of license limitations on TRYCACHE.

Well, maybe it's a handwritten response?

I'd recommend contacting the API developer and verifying that API responses would be indeed JSON.

Can you make the same call to the API using Postman and show the response?

It's very strange that API returns non-json response.

Does my code snippet throw the same error?

You can simplify your code to this:

set dynObj = {}.%FromJSON(objHttpResponse.Data)
set iter = dynObj.%GetIterator()
while iter.%GetNext(.key , .value )  {
       write "key = "_key_" , value = "_value,!

}

Also json is a string so in your code sample it won't have %FromJSON method.

What version are you on?

If it's 2016.2+ you can use dynamic objects.

Variables are local to the process.

1.Variables are defined or referenced via <var>, yes, but you can pass the values to the Installer from your script. For example, check MDX2JSON installer:

Set pVars("User")="web"
Set pVars("Password")="dsweb"
Set pVars("Namespace")="TEMP3"
Set pVars("Import")=1
Set pVars("SourceDir")="C:\temp\MDX2JSON\MDX2JSON"
Do ##class(MDX2JSON.Installer).setup(.pVars)

2. You set environment variable in cmd (Windows):

set NEWVAR=SOMETHING

And after that you can get it from installer with:

$system.Util.GetEnviron("NEWVAR")

They go through your web server (i.e. Apache, NodeJS, IIS) directly.

You can serve files via REST, from files or XDatas. Here's an example in WebTerminal app, but it can be generalized to server arbitrary files from FS.

That would work only in the cases where original reference to OREF exists, right?

i was able to convert the HttpResponse.Data to String and than to the Dynamic Object

You don't need to convert to string, pass stream to FromJSON method and it would work.

send a JSON data to a REST API.

Set tAge = 23
Set pRequest= {"name":"abcdefghi","salary":123,"age":(tAge) }

What version are you on? If 2016.2+ then you can convert JSON stream to dynamic object via:

set dynObj = {}.%FromJSON(req.HttpResponse.Data)

Check out PythonGateway project.

Done. Check isc.xades package.