What "specific commands" generates this error?

I'm not sure I understand your question, probably not.

If you need to transform a message and then apply/evaluate rules, then create two HL7 Routing Business Processes, each with a Routing Rule associated.

The first BP and associated rule transform the message and send it to the second BP where you can apply rules to the transformed message.

But....probably I did not understand the question! 😊

You already answered your question....in the question! 😊

From %SYS namespace, use the List class query in the Config.Namespaces class:

%SYS>Set ResultSet=##class(Config.Namespaces).ListFunc()
 
%SYS>Do ResultSet.%Display()
Namespace       Globals Routines        System Globals  System Routines LibraryTemp Storage
%ALL    %DEFAULTDB      %DEFAULTDB      IRISSYS IRISSYS IRISLIB IRISTEMP
%SYS    IRISSYS IRISSYS IRISSYS IRISSYS IRISLIB IRISTEMP
USER    USER    USER    IRISSYS IRISSYS IRISLIB IRISTEMP
 
5 Rows(s) Affected
%SYS>

 Or, if you prefer:

%SYS>Set statement=##class(%SQL.Statement).%New()
 
%SYS>Set status=statement.%PrepareClassQuery("Config.Namespaces","List")
 
%SYS>Set resultset=statement.%Execute()
 
%SYS>While resultset.%Next() {  Write resultset.%Get("Namespace"),$c(9),resultset.%Get("Globals"),$c(9),resultset.%Get("Routines"),!}
%ALL    %DEFAULTDB      %DEFAULTDB
%SYS    IRISSYS IRISSYS
USER    USER    USER
 
%SYS>

I'm not sure what you mean with "the nice argument documentation for the arguments".

Do you have an example?

Hi Luis, I've never used a BS witout the usual ProcessInput() call, anyway, from a BS you cannot call SendRequestAsync() with a response. If you need a response in a BS then you must call SendRequestSync().

Maybe (likely!) I misunderstood your question.

What do you mean with "But some other namespaces on the same server could be mapped to a different namespace or even mapped to itself." ?

A namespace cannot be mapped to another namespace.

A namespace definition consists of default database for globals, default database for "routines" (all code) and optionally global/package/routine mappings to different databases. (Plus some default system mapping)

Form the %SYS namespace you can use the List class query in the Config.MapRoutines class.

For example:

%SYS>Set ResultSet=##class(Config.MapRoutines).ListFunc("USER")
 
%SYS>d ResultSet.%Display()
Name    Routine Type    Database
MyTestRoutine   MyTestRoutine           TRAINING
 
1 Rows(s) Affected
%SYS>Write ResultSet.%ClassName(1)
%SQL.ClassQueryResultSet
%SYS>

WOW! Nice!

But...is there any reason why this is not documented?

When was it introduced?
A quick test shows it was not available in Caché based products, that is 2018 and is available in 2022.1.
At the moment I cannot test version 2019 to 2021.

To properly display the status use:

Set statusText=$system.Status.GetErrorText(status)

First I'd suggest to change:

 Set httpRequest.Server = "http://127.0.0.1:8080" 

to:

 Set httpRequest.Server = "127.0.0.1" 
 Set httpRequest.Port = "8080" 

I would also check the status after:

Set status = httpRequest.Post("/collect_patient_information")

And then try again.

Excellent! Well done 👏

And last but not least, don't forget to cleanup.

Who/when ^SPOOL is cleaned?
What part should I clean? Just a shameless Kill ^SPOOL ?

IMHO, in addition to @Alexey Maslov notes, that's another (good) reason why device 2, the spool device, has been log forgotten (and buried) for good.

You mention you need to connect to Ensemble but your product version says IRIS. I assume you need to connect to IRIS.

In Windows you can install IRIS ODBC drivers and in Control Panel create a DSN to connect to a IRIS Namespace. Then in SSMS follow the instructions to connect to an external database using an ODBC DSN (I have no experience on this).
Make sure you use the correct 32 or 64 bits driver and DSN definitions (in Windows you can define 32 or 64 bits DSN), I'm not sure if Microsoft SQL Server Management Studio (SSMS) is 32 or 64 bits application, find that out first.

Another option is to use IRIS JDBC drivers, make sure you install the correct Java JRE for the JDBC drivers you are using.

Since this is windows, maybe ODBC is more convenient.

I'd suggest to start with the documentation pages:

Defining and Using XData Blocks

XData Syntax and Keywords

There you can find a lot of info to start with, then if you need additional info come back with more specific questions.

I don't think this information is stored in Lookup Tables.

Only table name, key and value are stored.