I'd implement a custom datatype, something like:

Class Community.dt.IntJSON Extends %Integer
{

Parameter JSONTYPE = "string";
ClassMethod JSONToLogical(%val As %String) As %Integer [ CodeMode = expression, ServerOnly = 1 ]
{
..DisplayToLogical(%val)
}

ClassMethod LogicalToJSON(%val As %Integer) As %String [ CodeMode = expression, ServerOnly = 1 ]
{
..LogicalToDisplay(%val)
}

}

Then in your class:

Class Community.json.TestDT Extends (%RegisteredObject, %JSON.Adaptor)
{

Property something As Community.dt.IntJSON(DISPLAYLIST = ",OK,Error,Warning", VALUELIST = ",0,1,2") [ InitialExpression = 0 ];

ClassMethod RunMe()
{
      set obj = ..%New()
      set obj.something = 2
      do obj.%JSONExportToString(.string)
      write "JSON : " _ string,!

      write "Content  : " _ ..somethingLogicalToDisplay(obj.something),!!

      set obj2=..%New()
      do obj2.%JSONImport(string)
      write "Imported something value: ",obj2.something,!
}

}

Result:

EPTEST>d ##class(Community.json.TestDT).RunMe()
JSON : {"something":"Warning"}
Content  : Warning
 
Imported something value: 2

I manage systems that use IIS since more than 15 years and never experienced performance issues.

For a code that takes 15ms having service/call that takes 40ms total round trip to me is way too much (that's 25ms overhead !!).
We have SOAP services that respond in 10ms (local subnet, round trip measured from the caller/client).

I don't recall any special configuration in IIS.

What's the configuration of the Web/CSP Gateway?

"Edición y reenvio de mensajes"

It seems to me that you are trying to edit and resend a message.

"The message was not modified before it was forwarded."

If so, does just pressing the resend button (instead of edit and resend) works?

Do you get this error when you enter that page ("Edición y reenvio de mensajes") or after pressing the resend button in that page?

Please provide more context/details.

It seems you are trying to resend an HL7 message within a production from Management Portal.
Is this correct? Is the message being resent an HL7 message?

Has the message been modified before resending?

Is the HL7 message being resent properly and correctly displayed in the message trace?

@Shane Nowack , in the first table in your post, in the left column/list this two items:

SQL Best Practices Doc
Best Practices for Defining SQL Optimized Tables Through Persistent Classes

both link the same documentation page, is this correct or maybe one link is not correct?

I think it means that that particular segment has been modified

Did you checked this post:

Upcoming InterSystems Container Changes

I think in the sample you have inverted Old and New

What's the version of the "source" system?

Try using the button "Import Legacy" instead of "Import".

Upgrading what product, from what version, to what version?

Just guessing, please check this documentation:

About Creating a Custom CSP Login Page

And in particular the first step:

Ensure that the Web Gateway user (CSPSystem) has permissions to read the database for where the custom login page is located. Assign the desired database resource to an appropriate role, and then assign that role to the CSPSystem user.

I suspect that's too small, but there are MANY missing details to consider and I might be wrong.

gmheap documentation is here.

Note that for new installation the value is 0 (zero), in that case:

the system will configure the size of gmheap to be 3% of the total memory configured for global buffers. The minimum gmheap will be configured to is 307,200 KB (300 MB) and the maximum is 2,097,000 KB (2 GB)

So, your gmheap is about 1/3 of current default.

Beware that $System.SQL.Schema.SetDefault() sets the default schema (optionally) for a namespace systemwide, that is, for all processes, not only current process.

It seems that in your system the routine ST.int is missing, can you check if it's in the %SYS namespace?

ST.int is part of Ensemble, it should be there but apparently is not (has been deleted?).

Just curious, what's the value of gmheap?
You can find it in iris.cpf or in Management Portal, System Administration > Configuration > Additional Settings > Advanced Memory

CSPGateway not insllatted in inetbup

How do you check that?

If you select the option you have highlighted, then CSP Gateway will not be installed, if you don't change it, then it will be installed.
What option do you use when you install? (first dialog)

However, is this a new fresh install or an upgrade of an existing Ensemble instance?

It's long time I don't install Ensemble 2018, why are you still using Ensemble and not IRIS?

I just tested installing Ensemble 2018 and CSP Gateway is properly installed and configured.

When the setup kit is run the first dialog is:

Do you get the same dialog? What option you choose?
As you can see it is also possible to install only the CSP Gateway component.

If you choose Custom then this dialog is displayed:

As you can see the option to install CSP Gateway for IIS is there.

If I proceed to the install, at the end I have the CSP Gateway properly configured in C:\inetpub\CSPGateway

In order to help you, apart from saying that is not being installed, can you provide some information on what you are actually doing and what do you actually see/get during install?