what's the format of the file to import lookup table ?

There are two formats for LUT:

Old one:

<?xml version="1.0" encoding="UTF-8"?><Exportgenerator="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"><Documentname="LUT_NAME.LUT"><lookupTable><entrytable="LUT_NAME"key="KEY">VALUE</entry><entrytable="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 %occErrorswrite"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 nameset 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 importif$$$ISERR(sc) {
			write"New import failed. Trying legacy import",!
			set sc=##class(Ens.Util.LookupTable).%Import(tablePath)
			if$$$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:$$$ISERR(tSC) tSC
	Set tSC = $$$OKKill Select
	For  {
		Quit:'tRS.Next(.tSC)
		Set Name = tRS.Get("Name")
		If$E(Name,*-3,*)=".LUT" {
			Lock +^Ens.LookupTable(Name):2If '$TSet tSC = $$$ERROR($$$LockFailedToAcquireRead,$Name(^Ens.LookupTable(Name))) QuitSet Select($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
}