There are two formats for LUT:

Old one:

<?xml version="1.0" encoding="UTF-8"?>
<Export generator="IRIS" version="26" zv="IRIS for UNIX (Red Hat Enterprise Linux 7 for x86-64) 2022.1 (Build 209U)" ts="2024-03-03 06:05:36">
    <Document name="LUT_NAME.LUT">
        <lookupTable>
            <entry table="LUT_NAME" key="KEY">VALUE</entry>
            <entry table="LUT_NAME" key="KEY2">VALUE2</entry>
        </lookupTable>
    </Document>
</Export>

New one:

<?xml version="1.0"?>
<lookupTable>
    <entry table="LUT_NAME" key="KEY">VALUE</entry>
    <entry table="LUT_NAME" key="KEY2">NALUE2</entry>
</lookupTable>

Looks like you're importing old format using new importer. Here's the code to import both versions:

ClassMethod ImportLUT(dir)
{
	#include %occErrors
	write "Lookup Tables import from: " _ dir
	set rs = ##class(%File).FileSetFunc(dir, "*.xml;*.XML;*.lut;*.LUT")
	while rs.%Next() {
		set tablePath = rs.Get("Name")
		write "Importing: " _ tablePath,!
		// table is the full path, the last part (denoted by *) is the actual file name
		set tablePathNoExtension = $PIECE(tablePath, "/", *)
		// asking for $PIECE with just delimiter asks for the first part, thus ignore anything after the .
		set tablePathNoExtension = $PIECE(tablePathNoExtension, ".")
		write "Importing Lookup Table in " _ tablePathNoExtension,!
		// lookup table should be named the file name (without extension)
		//do ##class(Ens.Util.LookupTable).%ClearTable(tablePathNoExtension)
		
		// Try the new import first.
		set sc = ..ImportLUTFile(tablePath)
			
		// If we got an error, try legacy import
		if $$$ISERR(sc) {
			write "New import failed. Trying legacy import",!
			set sc=##class(Ens.Util.LookupTable).%Import(tablePath)
			if $$$ISOK(sc) {
				write "Import successful",!
			}
		}
		
		// Error remains unfixed. Fail.
		if $$$ISERR(sc) {
			write "Lookup Table import failure: ", $System.Status.GetErrorText(sc),!
			do $system.Process.Terminate(, 1)
		}
	}
}

/// Adapted from EnsPortal.LookupSettings:Import
/// Import lookup tables from file <var>Filename</var>
ClassMethod ImportLUTFile(Filename As %String) As %String
{
	Set tRS = ##class(%ResultSet).%New("%RoutineMgr:ImportItemList")
	Set tSC = tRS.Execute(Filename)
	Quit:$$$ISERR(tSC) tSC
	Set tSC = $$$OK
	Kill Select
	For  {
		Quit:'tRS.Next(.tSC)
		Set Name = tRS.Get("Name")
		If $E(Name,*-3,*)=".LUT" {
			Lock +^Ens.LookupTable(Name):2
			If '$T Set tSC = $$$ERROR($$$LockFailedToAcquireRead,$Name(^Ens.LookupTable(Name))) Quit
			Set Select($E(Name,1,*-4)) = ""
		}
	}
	Quit:$$$ISERR(tSC) tSC
	Quit:'$D(Select) $$$ERROR($$$GeneralError,"This file does not contain any lookup tables")
	Set tSC = $system.OBJ.Load(Filename,"-d", .Err, .Loaded, 0)
	Set Name = ""
	For  {
		Set Name = $O(Select(Name))
		Quit:Name=""
		Lock -^Ens.LookupTable(Name)
	}
	Quit tSC
}

You need to iterate on value:

 // extract json content from the request:
 set dynRequestJsonPayload = {}.%FromJSON(%request.Content)
 #dim JsonIterator As %Iterator.AbstractIterator
 set JsonIterator = dynRequestJsonPayload.%GetIterator()
 
 // iterate on json structure:
 if dynRequestJsonPayload '= "" {
    while JsonIterator.%GetNext(.key, .value, .NodeType) { 
      if NodeType = "string" {
        do GlobalTrace("NodeType: " _ NodeType _ "; key: " _ key _ "; value: " _ value)
      } elseif NodeType = "array" {
         // i want to iterate on this array...
         // the following line throws the exeception "ERREUR #5002: Erreur ObjectScript: &lt;INVALID OREF&gt;traitementUFI+34^common.REST.1"
         set JsonIteratorSecondary = value.%GetIterator()
      } else {
	      // Do something
      }

    }
}

You can set it programmatically:

set package = ##class(%PackageDefinition).%OpenId("User",,.sc)
 
zw package
package=2@%Library.PackageDefinition  ; <OREF>
+----------------- general information ---------------
|      oref value: 2
|      class name: %Library.PackageDefinition
|           %%OID: $lb("User","%Library.PackageDefinition")
| reference count: 2
+----------------- attribute values ------------------
|       %Concurrency = 1  <Set>
|         ClientName = ""
|        Description = ""
|       GlobalPrefix = ""
|               Name = "User"
|          OwnerName = ""
|          RtnPrefix = ""
|            SQLName = ""
+----------------- swizzled references ---------------
|             i%list = ""  <Set>
|             r%list = ""  <Set>
+-----------------------------------------------------

What's "RO" stand for?  

ReadOnly.

After the customer deployment, if there is any change made on the production settings (e.g. changing an AE Title on the DICOM service), those settings are stored in the APPCODE, and the settings will be lost after a container PODS restart (kubernetes recreating the PODS).

Two ways to avoid that: